GIS Midterm Review
Advantages of proportional symbol map
Can be useful to show multiple variables if used in graph format
Principles of Map Design
1) Purpose 2) Geographic space/expanse 3) available data 4) map scale 5) audience 6) conditions of use 7) technical limits 8) conventions and standards
Data Classification order
1. Equal intervals 2. Quantiles 3. Natural Breaks/optimal (jenks) 4. Mean/standard deviation 5. Manual 6. Geometric interval
Data are organized into 4 different levels
1. Nominal (Categorization) 2. Ordinal (Categorization & Ordering) 3. Interval (Ordering & Explicit Values, arbitrary zero) 4. `Ratio (Ordering & Explicit Values, non-arbitrary zero)
Map projection steps
1. Reduce the Earth's size to that of an imaginary globe 2. Project the graticule from the reference globe onto the developable surface
Spatial queries
A GIS lets you select spatial features based on their location relative to other spatial features. uses "select by location" tool
What is GIS?
A computerized system for capturing, storing, analyzing, visualizing & managing data, data which are spatially referenced.
Coordinate system
A coordinate system is a reference system used to represent the locations of geographic features, imagery, and observations such as GPS locations within a common geographic framework.
Datum
A datum defines the position of the spheroid/ellipsoid relative to the center of the earth. (ie It defines the origin and orientation of latitude and longitude lines.)
Mollweide Projection
An equal-area map which shows the correct size of landmasses in relation to other landmasses but distorts shape - ellipse
Disputed borders
Approximately 75% of the territories around the world have some form of territorial dispute e.g. China has 17 territorial disputes with its neighbours, on land & sea
Polygon example
Area features: Countries, states, oceans
Types of queries
Aspatial and Spatial
First maps
Babylon (600BC) Ptolemy's Map (150AD)
Can you name the early American public land surveyor and cartographer who drafted this map of a portion of the Ohio River in Pennsylvania in 1752?
George Washington
Line example
Linear features: roads, rivers, rails, etc
Disadvantages of proportional symbol map
Can become crowded on maps with small enumeration units
4 thematic mapping techniques
Choropleth Proportional Symbol Isarithmic Dot Mapping
Map projection characteristics
Class, Case, Aspect
Natural Breaks (Jenks)
Classes are based on natural groupings inherent in the data through examination of the histogram
Advantages of quantiles
Easy (manual) Calculation Allows use of the complete color spectrum
Advantages of equal intervals
Easy Calculation Easy Interpretation No Gaps
Three types of Coordinate Systems
Geographic coordinate systems Projected coordinate systems Grid Systems
Three types of coordinate systems
Geographic coordinate systems, Projected coordinate systems, Grid Systems
Projected Coordinate System
coordinate system that provides various methods to project the earth's spherical surface onto a two-dimensional Cartesian coordinate plane. Typically using feet or meters
Each geographic object in a vector layer - each city, river, lake, or country - is called a ______
feature
vector layers contain ________
features
UN Map
first version had 90 degrees west oriented vertically, now centers on 180 degrees, pointing upwards
three basic map types
general reference thematic special purpose
Geographic Coordinate System
global or spherical coordinate system such as latitude-longitude, typically expressed as Degrees Minutes Seconds (DD:MM:SS) or Decimal Degrees (DD).
Elements of Map Composition
map body inset/overview map title legend scale orientation/direction indicator map metadata
equidistant projection
map that maintains distance but distorts other properties
Dot mapping
one dot is set to be equal to a certain amount of phenomena, and ideally the dots are placed where that phenomena are most likely to occur
Conventional databases
only non-spatial entities
Conical projection example
perspective conic
Quantitative Data measurement
Ordinal (Categorization & Ordering) Interval (Ordering & Explicit Values, arbitrary zero) Ratio (Ordering & Explicit Values, non-arbitrary zero)
Planar projection example
Orthographic
Why do biases in maps matter?
People take maps at face value Influence decisions and behavior All maps represent some perspective
Spatial
Pertaining to the distribution, distance, direction, area, and other aspects of space on the Earth's surface
three basic map projections
Planar conical cylindrical
Point example
Point features: Monuments, points-of-interest, buildings, etc.
Featurescan take the form of _______________
Points, Lines and Polygons
Locations
Position in 2D space
Distortion
altering the size or shape of the earth's landmasses and graticule for projection to a flat or planar surface
Every Geographic Coordinate System includes
an angular unit of measure, a prime meridian, and a datum
Every Geographic Coordinate System includes:
an angular unit of measure, a prime meridian, and a datum
Model
an idealized and simplified representation of the world
Maps are an assertion of
power and administrative control
Visual Hierarchy
refers to the order of the graphical representation of your map information Helps in defining the figure-ground relationship
balance
refers to the organization of map elements and the empty space, resulting in visual harmony and equilibrium
Class
refers to the overall appearance of the graticule, once the projection process is complete Cylindrical, Conic or Planar
Case
relates to how the developable surface is positioned with respect to the reference globe Tangent or Secant
Databases
repository of structured information stored in tables of rows and columns.
Data model
set of constructs for representing objects and processes in the digital environment
Three Approximations of Earth
sphere, ellipsoid, geoid
You'll want to join two tables when:
the data in the tables has a one-to-one or a one-to-many relationship.
You'll want to relate two tables when:
the data in the tables have a many-to-one or many-to-many relationship
Layers are grouped by _____
theme
Rasterlayers contain a range of
values
_________ can take the form of optical, spectral and radiometric indicators
values
Layers can be ______ or _______
vector or raster
Make smart use of ___________ to make a map that is aesthetically pleasing and conveys the intended message effectively.
visual hierarchy, balance, contrast and colour
Relate
works with many-to-one and many-to-many relationships. Does not append tables. Instead, you can access the related data when you work with the layer's attributes.
Join
works with one-to-one and many-to-one relationships. Appends tables together into a new table.
Grid systems divided into ______ with only positive coordinate numbers (metres or feet)
zones
Isarithmic Map
(contour map) is created by interpolating a set of isolines between sample points of known values (example; contour map)
Each coordinate system is defined by:
-Its measurement framework, either geographic (3-D) or projected (planimetric) (2-D) -Unit of measurement -The definition of the map projection (for projected coordinate systems) -Other measurement system properties such as a spheroid (ellipsoid) of reference; a datum; and projection parameters like one or more standard parallels, a central meridian
Planar class
-Lines of longitude are straight, equally spaced that radiate from the center -Lines of latitude appear as concentric circles, centered about a point Again, The spacing of the parallels distinguishes one type of planer projection from another
Database Management System (DBMS)
-Manages the linkage between features and their attributes (i.e. the link between an object on the map and its description) -Manages interactions between clients and raw data -Manages different versions of data -Preserves data integrity -Provides secure access
Two Types of Data to be managed in GIS
-Spatial Data (where things are) -Tabular/Attribute data (what things are)
When would you use an Inset map?
1. To show a primary map area in relation to a larger more recognizable area 2. To enlarge important or congested areas 3. To show alternate thematic topics that are related to the maps theme, or different dates of the same theme
2 grid systems
1. Universal Transverse Mercator (UTM) 2. State Plane Coordinate System (SPCS)
Choosing the correct map projection
1. Which spatial properties do you want to preserve? 2. Where is the area you're mapping? Is your data in a polar region? An equatorial region? 3. What shape is the area you're mapping? Is it square? Is it wider in the east-west direction? 4. How big is the area you're mapping? On large-scale maps, such as street maps, distortion may be negligible because your map covers only a small part of the earth's surface. On small-scale maps, where a small distance on the map represents a considerable distance on the earth, distortion may have a bigger impact, especially if you use your map to compare or measure shape, area, or distance.
Waldseemuller Map
1507 - 1st map to depict Americas as their own continents - "BIRTH CERTIFICATE" of America
How many Spatial Relationships can be preserved or distorted by a particular map projection?
4 Relationship: area, angle, distance, direction Projection: Equivalent, or Equal Area, Conformal, Equidistant, Azimuthal Projections
grid system
A grid is placed over a map projection using a plane or Cartesian (x,y) coordinate system to locate features Created for larger scale mapping Divided into zones with only positive coordinate numbers (metres or feet) Easier to calculate area, direction and distance
Developable surface
A mathematically definable surface onto which the land masses and graticule are projected from the reference globe
Reference globe
A model of the earth at a reduced scale, that is used to project the landmasses and graticule onto a flat map
Reference map
A model of the earth at a reduced scale, that is used to project the landmasses and graticule onto a flat map
Raster
A representation of the world as a surface divided into a regular grid of cells.
vector
A representation of the world using points, lines, and polygons
Mercator Projection
A true conformal cylindrical map projection, the Mercator projection is particularly useful for navigation because it maintains accurate direction. Mercator projections are famous for their distortion in area that makes landmasses at the poles appear oversized.
What is chloropleth mapping suited to?
Abrupt Data Calculation of Typical Values (Ex. median income)
spatial queries
Adjacency Operations used to identify those features that "touch" other features. Containment Operations used to identify those features that "contain" or "surround" a set of target features
Spatial Queries are usually done based on two concepts:
Adjacency and containment
Robinson's guidelines
Conformal - Analyzing, measuring, recording angular relationships. Use for navigation, piloting, surveying Equivalent - Geographic comparisons across space. Use for thematic maps that represent proportions, either through color, or dot density Planar(Azimuthal) - Tracking the direction of movement Equidistant - Determination of distances
Advantages of mean (standard deviation)
Considers how data is distributed along the number line If data are normally distributed, then the Mean is a natural dividing point BUT ONLY works well for data that are normally distributed
Rasters are best for _____ data
Continuous
Disadvantage of natural breaks
Data ranges are usually uneven
Geographic Phenomena can be arranged along the following lines:
Discrete or continuous AND abrupt or smooth
Equal Intervals
Divides the range of attribute values into equal-sized sub ranges
Disadvantages of equal interval
Does not consider data distribution along the number line
Disadvantages of chloropleth mapping
Doesn't show variation WITHIN mapping unit Based on arbitrary boundaries
Cantino Planisphere
Early map of the Indies (Caribbean) and Africa made in 1502. It showed how skewed 16th Century Europeans' idea of geography was.
Quantiles
Equal numbers of observations are placed in each class
Pearson's guidelines
Equatorial Regions (0° to 30°N/S) - Cylindrical Mid Latitude (30°- 65°N/S) - Conic Polar Regions (Above 65°) - Planar
Disadvantages of quantiles
Identical Data values MAY be placed in different classes Again, fails to consider how data is distributed along the number line
attributes
Identity and Description. E.g. Qualities or Quantities, such as city names or population figures are stored in database tables often called Attribute Tables.
Dot mapping disadvantages
If you do not have access to ancillary information, such as satellite imagery, it is hard to have confidence in dot placement
Secant lines distortion
Inside secant lines: objects slightly smaller Outside secant lines: slightly bigger
Cold War Propaganda
It presents the USSR as looming over the world; it uses bellicose terminology such as "menace" and "vital" to enhance anti-communist sentiment. These maps use vivid images to create narratives supporting national interests by influencing the beliefs of their people.
when to use ellipsoid
Larger Scale maps of smaller areas
Conic class
Lines of longitude are straight lines of equal length, radiating from a central point (poles) Lines of latitude are concentric circular arcs centered around one of the poles Distinguishing Features -"Pie-Wedge"Shape -The angular extent of the wedge, and the spacing of the parallels distinguish one conic projection from another
Cylindrical Class
Lines of longitude are straight, equally spaced Lines of latitude are straight, parallel and intersect lines of longitude at right angels Distinguishing Features The spacing of the parallels distinguishes one type of cylindrical projection from another
DBs are used to
List, or Inventory Sort and order Compare Calculate & Synthesize
A GIS tracks ____ and ______
Location and attributes
The key function of a GIS is linking _____ to _______
Location to information
elements of all maps
Locations and Attributes
Cylndrical projection example
Mercator
Advantages of natural breaks
Minimizes the differences between data values in the same class, & maximize the differences between classes
Qualitative Data measurement
Nominal (Categorization)
Foreign Keys
Non-unique Identifier that carries information that may be linked to the primary key. often primary keys replicated in other tables and facilitate joins and relates between tables.
Queries
Primary method of data retrieval formed in SQL, are structured statements used to interrogate the database. Create new information from existing information, but won't change the older/existing information
Dot mapping suited to
Raw Data Totals
Proportional symbol map suited to
Raw Data Totals
when to use geoid
Reference surface for ground surveying of horizontal and vertical positions
Database Models
Relational Object-Oriented Object-Relational
Geodatabases
Requires assignment of Geographic or projected reference system upon creation. May be at the Feature Data Set or Feature Class Level
Queries are formed
SQL
Proportional Symbol Map
Scaling Symbols in proportion to the magnitude of the data around a central point. Can be used for actual or conceptual points.
Aspatial queries
Set Algebra <, >, =, <> Boolean Queries OR, AND, NOT
When to use sphere
Small scale maps, Countries, Continents
Isarithmic/Isopleth Mapping suited to
Smooth data totals
Considerations for Isarithmic/Isopleth Mapping
Standardization of Data Finer level of enumeration units more suitable
Considerations for chloropleth mapping
Standardization of Data (Unevenly sized Enumeration Units)
Data standardization
The numbers are distributed throughout the unit of analysis, and the size of the unit is taken into account. ie. raw data totals are adjusted for the size of the enumeration unit.
Mean: standard deviation
This classification scheme shows you how much a feature's attribute value varies from the mean.
Geometric interval
This is a classification scheme where the class breaks are based on class intervals that have a geometrical series An algorithm creates these geometrical intervals by minimizing the square sum of element per class Ensures that each class range has approximately the same number of values with each class and that the change between intervals is fairly consistent Produces a result that is visually appealing and cartographically comprehensive
primary key
Unique Identifier for EACH row of information a particular data file are unique and there is one for each record (row) in the database.
American Meridian
Used to determine State boundaries before Greenwich
Cloropleth Mapping
Used to portray data collected for Enumeration Units (counties, states, wards, districts etc)
Two types of GIS spatial data
Vector and raster
Grid systems
a grid placed over a map projection using a plane or Cartesian (x,y) coordinate system to locate features
spatial data model
a set of constructs for representing Geographical objects, data, processes, and relationships in the digital environment, for the purposes of analysis and complex problem solving
Isopleth Map
a special kind of isarithmic map in which the sample points are associated with enumeration units
Structured Query Language (SQL)
an international standard language for processing a database initially developed by the International Business Machines Corporation (IBM Corp) but is supported by a number of software vendors
Maps
are the visual representation of a spatial relationship between features
Features are linked to a row in the _______________
attribute table
In addition to location, features have _______ that identify and describe the features.
attributes
Aspect
deals with the placement of the projections center with respect to the earth's surface Equatorial, Polar, Oblique
datum
defines the position of the spheroid/ellipsoid relative to the center of the earth. (ie It defines the origin and orientation of latitude and longitude lines.)
Azimuthal
directions from a central point are preserved; usually these projections also have radial symmetry
Spatial Distribution of data
discrete or continuous abrupt or smooth
Disadvantage of Projected Coordinate System
distortion
continuous data examples
elevation, temperature, rainfall, etc.
Generic reference map
include various geographic features with no specific emphasis on any feature(s) or attribute(s)
Longitude
is an angular distance, East or West of a point on the Earth's surface, measured from the center of the earth
Latitude
is an angular distance, North or South of the Equator measured from the center of the earth
Cartography
is the making and study of maps in all their aspects
Relational databases make use of _____ to establish linkages between tables
keys
Grid systems created for _____ mapping
large scale
A map is made up of ______
layers
Relational databases
make use of keys to establish linkages between tables
