Digital Mapping Final
What is a Cartogram?
+A map made by distorting the geographic size of data collection units in proportion to their magnitudes. +Distorts the reality of a map to convey specific information. Distortion is based on the variable(s) being used. + A type of graphic that depicts attributes of geographic objects as the object's area. Area of places is represented by a magnitude of value instead of actual size
Contiguous Cartogram
+Also known as "density-equalizing" cartograms +Maintains proximity and contiguity +Results in extreme exaggeration of areas
Noncontiguous Cartogram
+Most common +Shape is preserved +Increases in size based on magnitude of attribute value
Understanding Cartogram Maps
+Must know the geographically correct map in order to effectively read and use a cartogram map. +If the distorted areas on a cartogram map are unfamiliar it will be difficult to use.
Challenges to creating Cartograms
+Shape +Topology (adjacency and connectivity) +Geographical appearance +Legibility
Retaining Spatial Characteristics
+Shape - makes it easier to relate a cartogram to a conventional map. +Proximity - nearness (topology) +Contiguity - boundary connectedness (topology)
Gridded Cartograms
+aka tessellating cartograms +Preserves topology (adjacency and connectivity) +Uses hexagons and squares Shapes remain uniform +Can be shaded using same classification/symbolization as choropleth maps
Pseudocontiguous Cartograms (Dorling Cartogram)
+geometric shape that is proportional in size to the magnitude variable being mapped +Easier to recognize patterns +Has some degree of contiguity
Jenks and Coulson's Classification Rules
1.Encompass the full range of the data. 2.Have neither overlapping values nor vacant classes. 3.Be great enough in number to avoid sacrificing the accuracy of the data, but not so numerous as to impute a greater degree of accuracy than is warranted by the nature of the collected data. 4.Divide the data into reasonably equal groups of observations.
Web maps can
1.Portray much larger geographic extents than the computer screen shows 2.Be Multiscale 3.Be real-time facets of information 4.Be interactive 5.Be dynamic
THE MAP PROJECTION PROCESS
1.The land elevation or sea depth of every point on the earth's surface is defined relative to the geoid surface; 2.The elevations and depths on the geoid are projected on the more regular ellipsoid surface to define the positions with geodetic latitude and longitude; 3.optionally, geodetic latitudes and longitudes may be converted into spherical coordinates for only small-scale maps; 4.finally, the ellipsoidal or spherical coordinates are transformed into planar (x,y) map coordinates through map projection equations.
Geographic Coordinate Systems
A geographic coordinate system (GCS)uses a three-dimensional spherical surface to define locations on the earth. A point is referenced by its longitude and latitude values. Longitude and latitude are angles measured from the Earth's center to a point on the earth's surface. The angles often are measured in degrees (or in grads).
WHAT IS GIS?
A geographic information system (GIS) is a framework for gathering, managing, and analyzing data. Rooted in the science of geography, GIS integrates many types of data. It analyzes spatial location and organizes layers of information into visualizations using maps and 3D scenes. With this unique capability, GIS reveals deeper insights into data, such as patterns, relationships, and situations—helping users make smarter decisions.
Ellipsoid
A mathematical model of the shape of the earth (a geometric figure calculated by rotating an ellipse. Same volume as geoid. ◦Ellipsoids are idealized surfaces (perfectly smooth) that are designed to approximate as close as possible the actual geoid. ◦Used to relate any geographic location to a standard reference system.
Basics of Thematic Map interpretation
A thematic map is a map that focuses on a specific idea or theme. A thematic map illustrates a particular subject and contrasted the general map, in which the variety of geological and geographical phenomena regularly appear together Thematic maps use the base data as coastlines, boundaries and places, only as points of reference for the phenomenon being mapped Thematic maps also emphasize spatial variation of one or a small number of geographic distributions. These distributions may be physical phenomena such as climate or human characteristics such as population density and health issues While general reference maps show where something is in space, thematic maps tell a story about that place. Thematic maps portray spatial variations and interrelationships of geographical distributions
Advantages/Disadvantages of Data Types
ADVANTAGES Ease of interpretation Ease of scaling Compact geometric form Ability to portray distribution of more than one thing DISADVANTAGES Inaccuracies in perception of symbol area/volume No zero value
GIS (Geographic Information System)
AGEOGRAPHIC INFORMATION SYSTEM(GIS) IS A SYSTEM DESIGNED TO CAPTURE, STORE, MANIPULATE, ANALYZE, MANAGE, AND PRESENT SPATIAL ORGEOGRAPHIC DATA GIS APPLICATIONS ARE TOOLS THAT ALLOW USERS TO CREATE INTERACTIVE QUERIES, ANALYZE SPATIAL INFORMATION, EDIT DATA IN MAPS, AND PRESENT THE RESULTS OF ALL THESE OPERATIONS. SINCE THE MID-1980S, GEOGRAPHIC INFORMATION SYSTEMS HAVE BECOME VALUABLE TOOL USED TO SUPPORT A VARIETY OF CITY AND REGIONAL PLANNING FUNCTIONS. •GIS can refer to a number of different technologies, processes, techniques and methods. It is attached to many operations and has many applications related to engineering, planning, management, transport/logistics, insurance, telecommunications, and business.
Apparent Magnitude Scaling
Adjusts symbol size to account for misinterpretation Based on experimental values Not consistent but better than nothing
Principles of Choropleth Mapping
Aggregated -Entire unit= one value Generally, Lighter is less of a quantity or less of the issue Darker is more of a quantity or more of the issue Typically, various saturation of one Color! Use multiple colors when it makes interpreting the data easier (better with interval) Classes and Class Breaks Represents a phenomenon (not a physical feature) as though it is a physical feature. Shades according to a variable in a dataset.
TISSOT'S INDICATRICES
Also called "ellipse of distortion". Used to assess the nature and degree of distortion in various projections. Indicatrices show how various projections distort representation of earth in two dimensions On the globe all the indicatrices are the same size and shape
Handling Symbol Overlap
Amount of overlap subjectively measured... but you don't want it either too full or too empty Try to find a balance
Mental Maps
An individual's internalized representation of aspects of Earth's surface. These maps in the mind are what a person knows about the locations and characteristics of places at a variety of scales, from the local (the layout of a person's bedroom) to the global (the distribution of oceans and continents across Earth). Mental maps are a mix of objective knowledge and subjective perceptions: precise knowledge about the location of geographic features as well as impressions of places, rough estimates of size and location, and a general sense of the connections between places.
SPATIAL DESCRIPTIVES: STANDARD DISTANCE
Analogous to the Standard Deviation, Standard Distance is a measure of how far points typically are from the Mean Center (star). In this case, we see about 65% of points are within a standard distance of the mean.
Small circle
Any circle on the earth's surface whose plane intersects the interior of the sphere at any location other than the center. Its circumference is smaller than a great circle.
Considerations: Symbol Selection
Any point symbol that can be scaled may be used Most common is a solid circle: ◦Compact ◦Easily scaled ◦Visually stable ◦No orientation
Map Scale
Appropriate scale is determined by: ◦Necessity -scale should be sufficient to accommodate symbol recognition ◦Available space -the size of the sheet. Too small and scale problems will occur; too large and you have extra space but no extra data
MAP PROPERTIES
Area-An equal-area map portrays areas over the entire map so that all mapped areas have the same proportional relationship to the areas on the Earth Shape-A conformal map preserves shape when local angles are preserved and the scale of any point on a map is the same in any direction Distance-A map is equidistant when it preserves distance from a point or line, achieved when scale remains constant Direction-A true direction projection map preserves direction when azimuths (angles from a point on a line to another point) are portrayed correctly in all directions
Georeferencing
Assigning geographic coordinates to an image. Georeferencing is crucial to making aerial and satellite imagery, usually raster images, useful for mapping as it explains how other data, such as the above GPS points, relate to the imagery. Very essential information may be contained in data or images that were produced at a different point of time. It may be desired either to combine or compare this data with that currently available. The latter can be used to analyze the changes in the features under study over a period of time. Different maps may use different projection systems. Georeferencing tools contain methods to combine and overlay these maps with minimum distortion. It may be required to establish the relationship between social survey results which have been coded with postal codes or street addresses and other geographic areas such as census zones or other areas used in public administration or service planning.
Data Types
Can be used for ratio data but not interval data ◦How to symbolize zero? ◦Negative data? Can use raw or normalized data ◦number of zombies or zombies/100,000pop. ◦total wheat production or percent wheat production Two types ◦Absolute scaling -size represents actual data values ◦Range scaling -size represents range (class) of values True point data :◦Measured at a point location ◦e.g.population of cities Conceptual point data :Collected over an area, but conceived as being located at a point for symbolization purposes
Replicative Symbols
Can make it hard to estimate magnitude Can make the map look cluttered Hard to understand if they overlap Keep map to one (or maybe 2 if dispersed) replicative symbols
Classification
Choropleth maps use data that have been classified Number of classes usually between 5 and 10, more likely 5 than 10 Classification methods vary depending on data and on the story you are telling ArcGIS includes several different classification schemes
BUT FIRST! WHAT IS DATA?
Collect observations about the real world Categorize your observations (Use five senses to observe Ask people questions in Philadelphia Record geographic coordinates, how important is it to you to be wealthy...) Organize observations (Summarize what you found Prepare data for examination) Analysis (examine relationships between data you observed What does the wealth variable have to do with how far someone's commute was Too many people have a long commute!) Make Decisions (Solve real world problems based on data collection and analysis How can we cut down on the commute? •Provide more jobs where people live •Provide more affordable housing in the city) ' DATA COLLECTION IS A RECURSIVE PROCESS!
WHAT IS SPATIAL DATA?: LINES
Composed of many (at least 2) vertices or points, that are connected Ex: roads, streams, walking route, etc
Decimal Degrees (DD)
Computers do not really work well with DMS coordinates and we really prefer the coordinates to be in Decimal Degrees or DD. This format allows us to perform standard decimal math operations on the coordinates. Even if you see DMS coordinates in a software package, the software will convert the coordinates to DD for calculations. We almost always need spatial data to be in Decimal Degrees in order to work with it on a computer. Sometimes computer software will convert coordinates from DMS to DD automatically. However, it's good to know the process to avoid any problems with the way DMS is expressed. ◦Latitude: 40.866389° ◦Longitude: -124.082778°
Issue 2: Ecological Fallacy
Confusion between individuals and groups Fallacy = error in reasoning The ecological fallacy occurs when you make conclusions about individuals based only on analyses of group data. As you aggregate data into groups, particularly for comparison, you lose the ability to say something accurate about the individual cases within a grouping
Equal Interval
Constant interval between classes - based on values along the x-axis Number of observations will be different from class to class Good if you want to make direct comparisons between different choropleth maps
Web Maps
Continuous Multi-Scale Pop Up Mash Up Real Time
MERCATOR
Cylindrical Preserves shape meaning feature outlines (like country boundaries) look the same on the map as they do on the earth Distorts area meaning the relative size of continents are distorted. Line of tangency: Equator
Peters
Cylindrical -Equal Area Preserves area meaning all continents have the correct size relative to each other Distorts shape meaning feature outlines (like country boundaries) look exaggerated on the map Line of tangency: Equator
Range Graded Symbols
Data are classed into groups(three to seven) A readily distinguishable symbol picked to represent each class; standard sets available Symbols are no longer proportional Appropriate classification scheme is an issue Data are lost
Coordinate Systems
Data is defined in both horizontal and vertical coordinate systems. Horizontal coordinate systems locate data across the surface of the Earth. Vertical coordinate systems locate the relative height or depth of data. Horizontal coordinate systems can be of three types: geographic, projected, and local. The default horizontal coordinate system is WGS 1984 Web Mercator.
Qualitative Data
Description of things that can be observed but not measured Distinguish and identify differences of kind aka Qualities
What is digital mapping?
Digital mapping (also called digital cartography) is the process by which a collection of data is compiled and formatted into a virtual image. The primary function of this technology is to produce maps that give accurate representations of a particular area, detailing major road arteries and other points of interest. The technology also allows the calculation of distances from one place to another.
Calculating Quantiles
Divide the count of features by the number of classes you want This will give you the number of features for each class Arrange your features from least to greatest value Divide them into classes so that the number of features in each class matches the result of your division equation
Calculating Jenks
Don't worry about this one It is a method of statistical data classification that partitions data into classes using an algorithm that calculates groupings of data values based on the data distribution. Jenks' optimization seeks to reduce variance within groups and maximize variance between groups.
Dynamic map
Dynamic: marked by usually continuous and productive activity or change. Digital Updatable Responsive Interactive
Appropriate Data
Enumeration units must be areal Attribute data must be quantitative Attribute data should be normalized e.g.rates or density ◦rates e.g. percent Hispanic ◦density e.g. population per square mile Assumes data is spread uniformly throughout enumeration unit
Quantile
Equal number of observations per class Because the number of observations will be the same from class to class, the interval between classes will be different Good classification scheme to use if certain statistical tests require equal numbers of observations
DATA COLLECTION (FIELD WORK)
Field work is the process of observing and collecting data about people, cultures, and natural environments. Field work is conducted in the wild of our everyday surroundings rather than in the semi-controlled environments of a labor classroom. Field work enables students and researchers to examine the way scientific theories interact with real life. Field work is important in both the social and natural sciences. Social sciences, such as economics or history, focus on people, culture, and society. Natural sciences, such as biology or chemistry, focus on physical characteristics of nature and natural environments.
Definition 1: Choropleth
From Greek:◦Choro = area or region◦Plethos = multitude A method of cartographic representation which employs distinctive color or shading applied to areas ... usually statistical or administrative areas.(International Cartographic Association)
Space:
Geographers examine how, why and with what effect diverse phenomena vary across the surface of the earth. Geographers understand space to be configured by the movement and organization of people and materials as well as being a location for social and material action.
Place
Geographers explore what places mean, how people shape places, and how places shape our lives. This brings many areas of geography together in an holistic approach to understanding the characteristics of, and relationships between localities, cities, regions, countries and continents.
Preliminary Considerations in Choropleth Mapping
Geographic Phenomena Number and Kind of Enumeration Units Map Scale Data Processing
What is Geography?
Geography is the study of place, space and the environment. Geography is unique in bridging the social sciences and natural sciences. Find out what makes our discipline essential in understanding the world in which we live. Geography is the study of places and the relationships between people and their environments. Geographers explore both the physical properties of Earth's surface and the human societies spread across it. They also examine how human culture interacts with the natural environment, and the way that locations and places can have an impact on people. Geography seeks to understand where things are found, why they are there, and how they develop and change over time. Geography is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and planets. Geography is an all-encompassing discipline that seeks an understanding of Earth and its human and natural complexities—not merely where objects are, but also how they have changed and come to be.
Geoprocessing
Geoprocessing is a GIS operation used to manipulate spatial data. A typical geoprocessing operation takes an input data set, performs an operation on that dataset, and returns the result of the operation as an output dataset. Common geoprocessing operations include geographic feature overlay, feature selection and analysis, topology processing, raster processing, and data conversion. Geoprocessing allows for definition, management, and analysis of information used to form decisions.
Web Maps Examples
Google Maps, Coronavirus Map
Data Normalization
Helpful to view data in tables or graphs -this helps the cartographer understand his data It is often necessary to calculate rates or density measures
Fields of knowledge
Humanities Natural Science Social Science Formal Science Applied Science
Thematic Maps:
Identify the spatial distribution of a particular theme, characteristic, or property
WHAT IS SPATIAL DATA?
Information about the locations and shapes of geographic features and the relationship between them, usually stored as coordinates and topology Topologies = geometry + locationi.e., points, lines, polygons Any data that can be mapped ESRI
Application Programming Interface (API)
Interface used by software components to communicate with each other Set of functions that allow for the creation of applications that access data and features of other applications, services or operating systems
Interval Data
Interval Classes show a range of values In this example the classes show a range of low elevations for states Notice the negative numbers - this is whythese values are interval scale, not ratio scale
Isopleth
Isopleth maps, also known as contour maps, depict smooth continuous phenomena such as precipitation.
Lines of tangency:
Line(s) along which the sheet of paper make contact with the globe. This is where the project is the most accurate
Choropleth Maps
Maps have been used to represent area for a long time More recent invention: displaying properties about areas Known as choropleth or thematic mapping
SPATIAL DESCRIPTIVES: MEAN CENTER
Mean Center (star) is the average location in a set of points. The longitude/latitude of the center is determined by finding the average longitude and average latitude of all the points separately.
Jenks - Natural Breaks
Minimizes variance within a class by dividing classes in areas where there are large breaks in the data Different sized classes, and different number of features Often the best choice for conveying information accurately to map readers Cannot be used to make direct comparisons between maps
Usage of Location Services
Modern websites and apps use location services for various purposes.
Nominal (also called Categorical)
Names or Categories No meaningful order Ex: Tree Species (Oak, Elm, Maple) •These data are just simple categorizations of things! No math involved!•No intrinsic order•No agreed way to rank from lowest to highest
Number and Kind of Enumeration Units
Number of units are related to scale More enumeration units = higher resolution, or greater detail Type and Size are determined by scale and questions to be answered Often determined by data available
Quantitative Data
Numerical / Computational Express differences of magnitude that can be expressed in numbers Measurement of Quantities
Ratio Scale Data
On a ratio scale, measurement has an absolute zero and the difference between numbers is significant ... Division makes sense A 50 kg person weighs half as much as a 100 kg person, so weight in kg is on a ratio scale
Interval Scale Data
On an interval scale, the difference (interval) between numbers is meaningful, but the numbering scale does not start at zero -i.e.no absolute zero Subtraction makes sense but division does not 200C is 100 degrees warmer than 100C, but you can't say that it is twice as hot ◦the time of day that each racer finished is measured on an interval scale
Interval
Order is meaningful, so is difference There is no meaningful zero Can do + or -, but not × or ÷ Ex: Temperature (in °C or °F) These have rank order, that is, you can rank them There are consistent, known spaces between these data points For example, 400F is warmer than 200F but 200F is not necessarily twice as cold as 400F These data do NOT have a 'true' zero. For example, 'temperature' is an interval level variable because there is no such thing as 'zero' temperature in the sense that there is no temperature Think about it this way: zero should mean a total absence of that quantity, such as zero rainfall.
Ordinal
Order is meaningfulDiff. between values not meaningful Can't do math on data Ex: House Addresses These data are 'ordered' Meaning, you can rank them, from lowest to highest, best to worst, etc However, spacing between the variables is unknown For example, I think that Wandavision is a more awesome show than The Flash, but I can't really quantify the difference in a mathematical way (that is, I can't say with any certainty that the Wandavision is 10 times better, or a 100 times) We can order these data, but there is never a consistent size difference between categories
Ratio
Order, diff, and ratio are meaningful Zero means none Can do all arithmetic: + - × ÷ Ex: Height Also have rank order Spacing and size differences between variables are consistent similar to interval But ratio level variables have a 'true' zero For example, rainfall, snowfall, crop yield When we say zero rainfall, it signifies that NO rain fell on the ground, or there was an absence of rain Can preform computation ➕➖✖➗
Ordinal Data
Ordinal Classes show relative values, not absolute values In this example, 1 is less than 3, but we don't know how much less it is Using numbers to label ordinal data is often confusing But be careful to use text that does not imply absolute values
Ordinal Scale Data
Ordinal Numbers establish order onlyIn the race, the finishing places of each racer, i.e., 1st place, 2nd place, 3rd place, are measured on an ordinal scale. The numbers mean something relative to each other, but we do not know how much time difference there is between each racer
Five Components of GIS
People Data Hardware Software Processes and Methods
How are maps made?
Physical (pen and paper, models) Electronic (Geographic Information Systems (GIS)Remote Sensing and/or Aerial Photography Web mapping Mashups)
CYLINDRICAL PROJECTIONS
Projection surface is a rectangle Scale is true along a tangent line or secant lines Mercator
PLANAR PROJECTIONS
Projection surface is circular Scale is true at the central point (tangent case) or along a circle (secant case) Often used to map polar regions
CONIC PROJECTIONS
Projection surface is fan-shaped Scale is true along standard parallel(s) Used for areas with east-west extent Lambert, Albers
Considerations: Multivariate Symbols
Proportional symbols, particularly circles, may be: ◦Color coded ◦Segmented into pie type charts ◦And inset (small circles inside of larger circles) In an attempt to portray multiple attributes
ROBINSON
Pseudo Cylindrical -'compromise projection Distorts both shape and area but minimally so. Not as extreme in distortion as Mercator and Peters Line of tangency: Equator
Quartiles
Quartiles divide an ordered dataset into four equal parts and refer to the values of the point between the quarters.
Ratio Scale Data
Ratio scale classes show a range of numeric values In this example the classes show a range of population for states Notice there are no negative numbers - therefore these values are ratio and not interval scale data Quantitative data that has an absolute zero - so both subtraction and division work
Modifiable Areal Unit Problem
Represents a phenomenon (not a physical feature) as though it is a physical feature. Shades according to a variable in a dataset. Are the units of aggregation the right ones? Example of MAUP: Gerrymandering
Considerations: Symbol Size
Research indicates that map-readers consistently underestimate the area or volume of geometric symbols Amount of error increases with symbol size Solutions: ◦Legend Design ◦Range graded symbols (classes) ◦Apparent magnitude scaling
INTERPRETING STANDARD DEVIATION (SD)
SDwill be small when all the data are close together The deviations from the mean Will be both positive and negative Sum will always be 0 SDis always 0 or a positive number s = 0 means no spread; as SDvalue increases, the spread of the data increases The units of SDare the same as the original observations SDis heavily influenced by outliers
Components of mental maps
Selection of information, details, labels Omission is as important as inclusion Proportions of sizes, scales, shapes Choice of physical or cultural features Relative placement of features Influence of personal experience Influence of media and world events Effect of core, periphery, semi-periphery
Reference Maps:
Show the location of easily observable physical features, such as political boundaries, major roads, cities, water bodies, etc.
Choropleth
Shows statistical data aggregated over predefined regions, such as counties or states, by coloring or shading these regions. For example, countries with higher rates of infant mortality might appear darker on a choropleth map. This technique assumes a relatively even distribution of the measured phenomenon within each region.
Examples of location services
Snapchat, uber, twitter, digital cameras, weather apps
DISPERSION: STANDARD DISTANCE
Standard Distance is a lot like the standard deviation It measures how close various locations are to the mean center. A high standard distance means points are more dispersed than a low standard distance. For example, X1has a lower standard distance that X2, because the point are closer on average to the centerX1
STANDARD DEVIATION (𝒔𝒔)
Standard deviation is a number used to tell how measurements for a group are spread out from the average (mean) or expected value. A low standard deviation means that most of the numbers are very close to the average. A high standard deviation means that the numbers are spread out.
Issue 1: MAUP
Stands for Modifiable Areal Unit Problem "MAUP refers to the fact that the observed aggregated values will vary according to how we draw our area boundaries"
Static map
Static: lacking in movement, action, or change, especially in a way viewed as undesirable or uninteresting. Physical or Digital Unchanging Fixed Unresponsive
Measures of spread
Statistics that describe how similar or varied the set of values are for a distributionRangePercentileAbsolute deviationVarianceStandard deviation
Measures of central tendency
Statistics that describe the central or typical value for a distributionMeanMedianMode
Calculating Equal Interval
Subtract minimum value from maximum value Divide the result of this subtraction by the number of classes you want The result of the division will be the width of each class Start with the minimum and add this value to get the width of the first class Continue adding this value to the sum of the previous class until all classes have been created
Spatial Data Characteristics of Proportional Symbol Maps
Symbol varies from place to place in proportion to the quantity it represents Typically used when dealing with point data, but can be used with aggregated data for polygons Size of point symbols vary with data values-length, height, area, volume Can also be used for line symbols (width)
Considerations: Symbol Placement
Symbols representing enumeration areas should be: ◦Located at geometric center of enumeration area ◦With exceptions for ease of placement and polygon shapes with geometric center outside of the enumeration area Symbols representing discrete point features: ◦Located at actual geographic coordinate ◦Not normally adjusted for placement
WHY MAPS INSTEAD OF GLOBES?
The Earth's surface is curved Projections make the curved surface flat. Projected maps are flat, compact, portable, and useful BUT DISTORTED
Compromise Projections:
The Winkel-Tripel A map projection that is neither equal area, conformal, nor equidistant, but rather a balance between these geometric properties. Used in thematic mapping.
DESCRIPTIVE STATISTICS
The analysis of data that helps describe, show, or summarize data in a meaningful way.measures of central tendency measures of spreadMakesit easier for you to find patterns in distributions
secant case:
The case that occurs when the developable surface cuts through the globe at either a circle of tangency (for planar projections) or along two lines of tangency (for conic and cylindrical projections).
tangent case
The case that occurs when the developable surface touches theglobe at either a point of tangency for planar projections or along a line of tangency for conic and cylindrical projections.
Absolute location
The exact location on the planet where something resides, or the latitude and longitude of a place. Physical measurement of the distance between two absolute locations. •For example, the Empire State Building is located at 40.7 degrees north (latitude), 74 degrees west (longitude). It sits at the intersection of 33rd Street and Fifth Avenue in New York City, New York. That is the building's absolute location.
TANGENT VS. SECANT PROJECTIONS
The first step in projecting from one surface to another is creating one or more points of contact. Each contact is called a point (or line) of tangency. A planar projection is tangential to the globe at one point. Tangential cones and cylinders touch the globe along a line. If the projection surface intersects the globe instead of merely touching its surface, the resulting projection is a secant rather than a tangent case. Whether the contact is tangent or secant, the contact points or lines are significant because they define locations of zero distortion. In general, distortion increases with the distance from the point of contact.
Interquartile Range
The interquartile range (IQR) is the difference between the upper (Q3) and lower (Q1) quartiles and describes the middle 50% of values when ordered from lowest to highest. The IQR is often seen as a better measure of spread than the range as it is not affected by outliers.
Great circle:
The largest possible circle that can be drawn on the surface of the spherical earth. Its circumference is that of the sphere, and its center is the center of the earth. All great circles divide the earth into halves.
Relative Location
The location of a place in relation to another place; a description of how a place is related to other places. Description of how connected or disconnected two locations are from each other socially, culturally, economically, etc. •For example, the Empire State Building is 365 kilometers (227 miles) north of the White House in Washington, D.C. It is also about 15 blocks from New York's Central Park. These are just two of the building's relative locations. Relative location can help analyze how two places are connected, whether by distance, culture, or even technology.
Mean
The mean is the sum of the value of each observation in a dataset divided by the number of observations. This is also known as the arithmetic average.
Median
The median is the middle value in distribution when the values are arranged in ascending or descending order.
Mode
The mode is the most commonly occurring value in a distribution.
Definition 3: Data Normalization
The process of dividing one numeric attribute value by another to minimize differences in values based on the size of areas or the number of features in each area. For example, normalizing (dividing) total population by total area yields population per unit area, or density
Data Classification
The process of sorting or arranging entities into groups or categories On a map, the process of representing members of a group by the same symbol, usually defined in a legend. When there are too many data values on a map it can lose its power to tell a story or make a point Most maps use data that have been classified Number of classes is usually between 5 and 10, more likely 5 than 10 Classification methods vary depending on data and on the storyyou are telling ArcGIS includes several different classification schemes Best carried out in the context of a histogram
Definition 4: Data Classification
The process of sorting or arranging entities into groups or categories; on a map, the process of representing members of a group by the same symbol, usually defined in a legend.
Proportional Symbol
The proportional symbol technique uses symbols of different sizes to represent data associated with different areas or locations within the map. For example, a disc may be shown at the location of each city in a map, with the area of the disc being proportional to the population of the city.
Range
The range is the difference between the smallest value and the largest value in a dataset.
Advantages of Digital Maps
The roots of digital mapping lie within traditional paper maps. Paper maps provide basic landscapes similar to digitized road maps, yet are often cumbersome, cover only a designated area, and lack many specific details such as road blocks. There is no way to "update" a paper map except to obtain a new version. Digital maps, in many cases, can be updated through synchronization with updates from company servers.
standard parallel:
The small-circle line or lines of tangency, usually at the mid-latitudes, that touch, in the tangent case, or intersect, in the secant case, the globe. A standard parallel has no distortion. A tangent conic or cylindrical projection has one standard parallel, while a secant conic or cylindrical projection has two.
Definition 2: Enumeration Units
The spatial extent, or area in which data were collected (enumerated). For example, US census data is collected in a variety of spatial units, including blocks, block groups, and tracts. Geometry = Enumeration Units
Cartography
The study and practice of making maps. Combining science, aesthetics, and technique, cartography builds on the premise that reality can be modeled in ways that communicate spatial information effectively. •At its core, cartography is about the visual representation of a space or place. While this may seem like a simple concept at first glance, it can become infinitely complex when you consider the number of choices that have to be made when creating a map.
Geoid
The surface of the Earth's gravitational field. Essentially a "lumpy" model of what sea level would look like if land masses allowed seas to settle based on gravitational pull (and gravity pulls unevenly!) Our best approximation of the globe is a geoid ◦Standard of equal gravitation pull ◦The shape of the earth without land or sea level around the globe
VARIANCE AND STANDARD DEVIATION
The variance and the standard deviation are measures of the spread of the data around the mean. They summarize how close each observed data value is to the mean value. In datasets with a small spread all values are very close to the mean, resulting in a small variance and standard deviation. Where a dataset is more dispersed, values are spread further away from the mean, leading to a larger variance and standard deviation. The smaller the variance and standard deviation, the more the mean value is indicative of the whole dataset. Therefore, if all values of a dataset are the same, the standard deviation and variance are zero.
When to Use Choropleth Maps
Theme in well defined enumeration units Data must work as ratios or proportions Not necessary to portray actual values in each enumeration unit Simplified data assumptions must be acceptable to map maker and map reader
Nominal, or Categorical Data
There are no absolute rules for this kind of classification, just general guidelines : ◦Features in different classes or categories should be more dissimilar than similar and should be symbolized differently ◦Features in the same class or category should be more similar than dissimilar and should be symbolized similarly
Discrete measures
Things that can be expressed using a limited, specific range of values and cannot be more precise. Discrete data usually involves whole integers (1, 2, 3, 4); or can often simply be pass/fail or good/bad assessments.
Dot Density
This type of map uses dots to locate a phenomenon. The density of the dots (how many/how few) in a particular region indicates the intensity of the phenomena. In this map for example, 1 dot=120 persons.
WHAT IS SPATIAL DATA?: POLYGONS
Three or more vertices that are connected and closed Ex: building boundaries, lakes, census tracts, states, countries
Mapping Issues
To portray a three-dimensional world on a flat surface, a map must distort reality. As a scale model, the map must use symbols, that are almost always much bigger or thicker than the things they represent. The map must offer a selective, incomplete view of reality.
WHAT IS SPATIAL DATA?: POINTS
Typically expressed as coordinates (Latitude, Longitude) Plotting location
To use or not to use Data?
USE WHEN 1.When objective is to show spatial variations in value/magnitude at point locations 2.For mapping aggregated data represented by a point NOT THE BEST CHOICE WHEN: 1.The range of data values is limited -i.e.boring 2.Interval level data are used ◦how would you map a value of 0 degrees Celsius ◦the circle for 10 degrees would be twice the size of a circle for 5 degrees 3.Data normalized by area This works, but you should seriously consider using a choropleth map
Data Classification and Legends
We covered data classification schemes previously List enumeration units Modify legend values if necessary Best to have multiples of 25, or 50, or 100 Try to change class values as little as possible
Choropleth Mapping
What you need: ◦Geometry -polygons ◦Quantifiable attribute/s ◦(Almost always )normalized data (for example, data expressed as a rate or density) ◦Classified data What you do ◦Determine symbolization ◦Normalize data ◦Classify Data ◦Graduated color ◦Identify patterns in the data
Graticule
a network of lines representing meridians and parallels, on which a map or plan can be represented
Economy, Culture, and Society
a social science distinguished by its attention to the relation of humanity to the earth, in two regards. The first concerns the interaction of people with nature, including the extraction of natural resources, the environmental impact of people and their activities, and the effects of natural forces on society. The second concerns the spatial organization of societies at all scales from the local to the global (and from minutes to millennia) and the production of place, territory and landscape by human imagination and activity.
A DATA TABLE
a)Rows: each person with whom we had a conversation gets a row. Put another way, each row in a data table is a logical entity of the same type as every other row. Rows are also called features, observations, or records. They all mean the same thing. b)Columns: each question we ask gets a column. These are often called attribute fields, fields, variables. c)Attributes: Each cell is the particular response to a given question for a given record. d)Header Row: Note that the first row is special. It provides the names for each of the columns in the data table. e)Unique Identifier (or Key): Each row has a field that identifies it and it alone. They do not and must not repeat.
Population:
all members of a specified group. Population is the whole group.
Variance (𝒔𝒔𝟐𝟐)
average of the squared deviations from the mean.
Continuous measures
can take on any value across a consistent scale and can be reduced to finer & finer results. continuous data can take any value on the real number line while discrete data generally are integer values.
MAP PROJECTIONS
map projection is essentially a way of representing our 3D Earth (a spheroid in shaped) on a 2 D surface (the map) When we do this, our flattened map representation of the Earth causes all kinds of distortions-areas, distances, shapes, sizes and directions of geographic places can all be distorted To deal with these distortions, we choose what are known as 'map projections' But projections are also not perfect-each projection distorts something while preserving something else! a means to depict the spherical earth on a two dimensional medium (i.e., based on spherical coordinate system, converted to a plane)Problem: the earth is not flat.
There are nine standard classification schemes:
natural breaks, optimization, nested means, mean and standard deviation, equal interval, quantile, arithmetic, geometric, and user defined Creating classes based on these schemes requires summary statistics and calculations - some simple and some difficult We will look at equal interval, quantile, standard deviation, and natural breaks
Sample
part of a population that is used to describe the characteristics of the whole population. A portion of the population, never the whole population.
Earth System Sciencr
the study of the interconnected components of our environment—the atmosphere, hydrosphere, lithosphere, cryosphere, and biosphere—and how they interact to produce an integrated whole.It utilizes the fundamental disciplines of mathematics, physics, chemistry, and biology and applies them in the context of human activities and landscapes to understand the Earth, at scales ranging from single watersheds to the entire globe.
Geodetic Datum
uses ellipsoid model as a reference point for a coordinate system (For example, origin at 0,0). Takes local variations in elevation into account to define difference in coordinates based on unevenness of Earth's surface. Different datums measure locations differently (e.g., below coordinates for Bellingham, WA in different datums
What is a Map?
•A map is a symbolic depiction emphasizing relationships between elements of some space, such as objects, regions, or themes. •A map is a symbolic representation of selected characteristics of a place, usually drawn on a flat surface.
What is web mapping?
•An interactive display of geographic information, usually in the form of a web page, that you can use to tell stories and answer questions .•A map presented in an online environment that includes not only the map, but also related content with an appropriate user interface and optional functionality for queries and reports.
Open-Source Libraries
•Application software that can be accessed and source code modified by the general public. •JavaScript Libraries is commonly used by open source web mapping applications. -OpenLayers -Leaflet -GeoServer -GeoMajas
Human geography sub disciplines
•Cultural Geography •Economic Geography •Health Geography •Political Geography •Population Geography •Transportation Geography •Urban Geography
What is web mapping used for?
•Data Visualization and Journalism -Urban Planning Maps -Migration Maps -Officer Involved Shootings Maps •Real-Time Spatial Data -Global Weather -Subway Transit Maps -Flight Maps •Online Catalogues and Search Computational Tools -Geojson.io -Mapshaper •Reporting and Collaboration -OpenStreetMap -Transitland
DOGSTAILS
•Date: Describes when the map was made or published •Orientation: Depicts the cardinal directions •Grid: Lines which help locate places on the map •Scale: Describes how much physical space is represented on the map •Title: Describes what is the map called •Author: Describes who made the map •Index: List of places on the map •Legend: Describes what the symbols on the map represent •Source: Describes where the information for the map came from
Physical geography sub disciplines
•Geomorphology •Hydrology •Glaciology •Biogeography •Climatology •Meteorology •Oceanography
Elements of GIS
•Graphic Elements •Points, Lines, Polygons, Pixels •Attribute Elements •Tabular data •Geographic Parameters •Coordinate Systems, Projections •Spatial Relationships (Topology) •Adjacency, Connectivity, Containment •Metadata •Data about data
Large-and Small-Scale Maps
•Large scale / Small scale distinction is based on the representative fraction •Large scale maps have a relatively large representative fraction compared to small scale maps: •1:1000 = .001 is larger scale •1:10,000 = .0001 is smaller scale (think about the denominator-the larger the denominator, the smaller the scale) •Small scale maps: don't show much detail, are very generalized •Large scale maps: typically show lots of detail (think of these as zoomed in maps)
Measuring Longitude and Latitude
•Latitude and longitude values are traditionally measured either in decimal degrees or in degrees, minutes, and seconds (DMS). •Latitude values are measured relative to the equator and range from-90°at the South Pole to +90°at the North Pole. •Longitude values are measured relative to the prime meridian and they range from -180°when traveling west to 180°when traveling east.
Location Services
•Location services rely on the Global Positioning System (GPS) to calculate your current coordinates. •GPS is run by the US Government •It is based on a network of satellites that orbiting the Earth. •Using signals from GPS satellites, GPS receivers such as smart phones can calculate your exact coordinates to great precision. •GPS does not require access to the internet. During the 1990s, GPS employed a feature called Selective Availability that intentionally degraded civilian accuracy on a global basis. •In May 2000, at the direction of President Bill Clinton, the U.S. government ended its use of Selective Availability in order to make GPS more responsive to civil and commercial users worldwide.
How do people use web maps?
•Navigation and Wayfinding -Google Maps -Apple Maps -Bing Maps -MapQuest •Journalism and News -New York Times -CNN -Washington Post -BBC •Advocacy, Reporting, and Collaboration -OpenStreetMaps -Uebermaps.com •Search for Information (location-based services) -Location of Business, services, or Point of Interest -Dark Sky -Pokémon Go -Emergency Services •Spatial Data Analysis -ArcGIS Online
Map Scale
•One of the major contributions that geography makes to the understanding of events, patterns, and phenomena is the concept of scale •Scale is the relationship between distance on the map and distance on the ground; it tells you about the size of an object on a map compared to the actual object on the ground •For example, a distance of 1000 feet on the ground might be represented as 1 inch on a map •In this case, the map scale will be: 1 inch = 1000 feet •Maps are always smaller than the portion of the Earth's surface they portray, hence the need for scale
GPS Alternatives
•Some other countries have their own systems. •Beidou-system deployed and operated by the People's Republic of China's, initiating global services in 2019. •Galileo-a global system being developed by the European Union and other partner countries, which began operation in 2016, and is expected to be fully deployed by 2020. •GLONASS-Russia's global navigation system. Fully operational worldwide. •IRNSS-A regional navigation system developed by the Indian Space Research Organization. •QZSS-A regional navigation system receivable in the Asia-Oceania regions, with a focus on Japan.
Spatial Analysis
•The true power of GIS lies in the ability to perform analysis. •Spatial analysis is a process in which you model problems geographically, derive results by computer processing, and then explore and examine those results. •This type of analysis has proven to be highly effective for evaluating the geographic suitability of certain locations for specific purposes, estimating and predicting outcomes, interpreting and understanding change, detecting important patterns hidden in your information, and much more.
Examples of APIs
•Tickets and Travel Booking •Enter your desired travel plans, provide your information, such as name and payment, then you receive your ticket after you complete the transaction. •JAVA •Microsoft .NET Framework •Free and Open-Source Software (FOSS)
Geoidal variation
◦Because of geoidal variation in the Earth's shape, different ellipsoids are used in different parts of the world. ◦It is important to select the ellipsoid that best fits the geoid at the region of interest. ◦Keep this in mind for later when we learn about projections and why different projects are used in different parts of the world.
Considerations: Symbol Selection (If more than one distribution is represented:)
◦Best to use same abstract symbol but different color hue ◦Not different color saturation or value ◦Different shapes are not recommended since comparisons are more difficult ◦Unless they are replicative and carefully scaled (This almost never works, but there is an example coming up of when it can work.)
Apparent magnitude scaling
◦Correction factors applied to compensate for map readers' underestimation of symbol's area or volume
Degrees Minutes Seconds (DMS)
◦Degrees, Minutes, and Seconds, or DMS, is the oldest format for geographic coordinates and you will still see this format in use on paper and even in movies where navigators will give their location in DMS. ◦Degrees for DMS are divided into 60 minutes and then each minute is divided into 60 seconds. This is just like the hours on our clocks and goes back to the Babylonians who worked with a base 60 number system! ◦Each degree contains 60 minutes ◦Each minute contains 60 seconds. One of the issues with DMS is that you will see them expressed in a variety of ways. ◦Latitude: 40°51' 59" N ◦Longitude: 124°4' 58" W
Converting from DMS to DD
◦First, recognize that: ◦60 minutes = one degree ◦60 seconds = one minute ◦3600 seconds = one degree ◦Using this, we can convert between DMS and DD with the equation: ◦DD = Degrees + (Minutes/60) + (Seconds/3600) ◦Converting between DD and DMS is now easy with the one addition that we need to remember that latitudes in the southern hemisphere are negative while longitudes in the western hemisphere (where most of the US is) are negative.
Map Scale: Types
◦Graphic scale: line or bar on map represents some set distance ◦Verbal scales: describes the scale of the map in words ◦Ratio scales/Representative fraction: a proportion between map distance and Earth distance ◦1/x = map distance/ground distance ◦Scale denominator x = ground distance/map distance
Latitude
◦Latitude has an astronomical basis. 0°latitude is the equator, which is the midpoint of the ecliptic, the sun's apparent path each solar year. ◦Latitudes run from 0°at the equator to 90°at each pole. The North Pole is 90°north; the South, 90°south.
Longitude
◦Longitude has no natural or astronomical basis. The earth is divided into 360°degrees, that run from pole to pole. ◦0°longitude is the Prime Meridian, which runs through Greenwich, UK. ◦Longitude ranges from 0°at the Prime Meridian to 180°at the opposite side of the Earth. Measurements of locations are said to be either east or west of the Prime Meridian.
Longitude Examples
◦Meridians ◦0-180 degrees ◦Run North to South ◦Measure East to West ◦Prime Meridian (Greenwich) -00
Latitude Examples
◦Parallels ◦0-90 degrees ◦Run East to West ◦Measure North to South ◦Equator 00 ◦North Pole -N900 ◦South Pole -S900 ◦Tropic of Cancer -N23.50 ◦Tropic of Capricorn -S23.50
Range grading
◦Symbol represents a range of data values
Absolute Scaling
◦Symbols are scaled proportionally to their data values, and are therefore in proportion to each other ◦i.e.if a symbol is 2x larger than another, it represents a value that is 2x larger
What is appealing about data analysis and visualization?
➢Promise of truth telling through objectivity ➢Make a complex and intimidating world stable ➢Numbers can be used to make demands
