Intro to GIS
Raster model
A format for storing, processing, and displaying graphic data in which graphic images are stored as values for uniform grid cells or pixels
Planimetric Map
A map that presents only the relative horizontal positions of natural or cultural features
Mixed Pixel
A pixel which contains multiple attributes for a single ground extent of a grid cell. These are common along the edges of features, or in places where features are poorly defined.
Azimuthal projection
A projection taken by projecting onto a plane. This type of projection is primarily used for polar regions.
GIS
A special kind of information system which is used to capture, manipulate, summarize etc. GIS(science) is the science behind the technology and considers fundamental questions raised by the use of systems and technologies
transformation vs projections
A transformation typically employs a statistically-fit linear equation to convert coordinates from one cartesian system to another, in a transformation, relative coordinates are absolute. On the other hand, a projection is an analytical, formula-based conversion between coordinate systems, usually from a curved system to the cartesian system, projections involve no statistical fitting.
GIS Data Analysis
Analysts can use different GIS functions and data to understand important patterns and trends in spatial data.
What is a map?
Any concrete or abstract representation of the distributions and features that occur on or near the surface of the earth or other celestial bodies
State plane coordinate systems
Are used by each state for accurate surveying. Locations expressed in feet to the east and north of an origin identified by each state.
Types of geographic data
Attribute and temporal
Storing attribute data
Attribute data is stored separately from the coordinate data. The feature identifier points are added to an attribute table (there can be a point, line/arc, or polygon attribute table). When we store attribute data, we try to avoid redundancy by creating a relational database through the normalization process which separates variables into several files.
Vectorization (Automated Digitizing)
Automatic digitizing uses tools to automatically convert a raster scan to vector lines. The scan must be very clean for a good image to be produced. The vector files typically will need to be cleaned after the conversion. If the image you have is not clean, than manual digitizing may be faster.
Raster structure
Data are stored in a grid of columns and rows. The intersection of each row and column is called a cell. Each cell corresponds to x and y coordinates in the real world and contains a z value that can represent all types of phenomena.
Attribute Data
Data linked to the spatial objects to describe properties, characteristics of spatial objects I.e. Land use categories, vegetation classes, ranking of small medium and large towns
Interval data
Data that has no true zero but is numerical
"The Matter of a Degree" article
Described how earth's shape was determined/discovered. Newton's concept of centrifugal force led him to the conclusion that the earth was an oblate spheroid. This challenged the idea that earth was a perfect spheroid.
Spatial Data
Describes locations positions, spatial extent of objects or entities that are referenced by location. · The spatial component of this type of data allows GIS users to map the location of features and perform spatial analysis.
Differential GPS
Differential GPS uses a base station of known coordinate positions to calculate errors introduced by slight deviations in the satellite's orbits and the atmosphere.
Discrete geographic features
Features in the form of points, lines or areas. These features have a clearly defined beginning and end. These types of features are best expressed using a vector model
Data capture techniques include
First hand or primary GIS sources, which include remote sensing images, GPS data and survey data. Or primary sources, those which are collected directly in digital format, specifically for GIS use.
Strengths of the vector model
For one, the point to line to polygon format is familiar to most people. Additionally, vector systems have small storage requirements which can make them easy to use and share. Additionally, it is helpful that individual features can be retrieved as individual objects for processing. It is also helpful that a variety of descriptive data can be associated with a single feature. Ultimately, vector models produce more correct cartographic products.
GIS coordinate transformation capabilities
GIS can translate or transform different coordinate systems into the coordinate system of choice. This allows for the combination of data from disparate sources into a common coordinate framework.
GIS Community
GIS has web pages, network conference groups, professional organizations, and user groups. All of these allow for GIS analysts to communicate with one another and learn and share ideas.
GNSS
GNSS is a Global Navigation Satellite System, which is a general term describing any satellite constellation that provides positioning, navigation and timing services on a global or regional basis. Several over countries have developed their own Global Positioning System. This name has been adopted to distinguish the concept and tool from the US system. GNSS systems include Russian GLONASS, European Galileo, Chinese Compass Navigation Satellite System.
History of GPS
GPS is the Global Positioning System (GPS), which is a satellite-based system that is used to calculate a three-dimensional position (longitude, latitude, altitude) on the Earth's surface. History of GPS: GPS began as LORAN (long range navigation) in the 1940s and it was used for marine navigation. Then in the 1960s, the United States began to develop satellite-based systems. In 1973 NAVSTAR GPS first satellite was launched. In 1983 GPS was declassified following a civilian aircraft accident. In the 1990's the US Department of Defense dedicated to $12 billion to the creation of a long-range navigational system. In 1994 the 24th satellite was launched and the NAVSTAR was fully operational. In 2000, the full features of GPS were available to commercial and civil users.
GPS
Global positioning System is a U.S.-owned utility that provides users with position, navigation, and timing services. It consists of a constellation of 24 to 32 satellites that operate in six different orbits.
Gall Peter's Projection
Highlights the developing world and areas that typically need aid. Preserves area. Has been adopted by global agencies such as UNICEF
Disadvantages of primary data collection through raster
In raster, often the spatial resolution of data is too course and many sensors can be restricted by weather conditions (i.e. cloud cover)
Advantages of primary data capture through raster
In raster, there is a consistency of data due to continuous observations. Additionally, there is broad availability of systematic global coverage. There are also regular repeat cycles and the measurement of various characteristics of geographic objects (spectral resolution)
Surveying
In surveying, the locations of objects are determined by angle and distance measurements from known locations. This way of collecting primary data uses expensive field equipment and crews. This is the most accurate method for large scale, small areas.
GIS Data Collection Function
In the data collection phase, the researcher will use a field instrument such as a sub-meter GPS unit to gather field data. This data will be translated into vector features and will then be merged with a geodatabase. From there, the data will be available for client use and the use of the GIS community.
Strengths of raster model
In the raster model, geographic position is implicit. Additionally, neighboring locations are represented by neighboring cells. The raster model accommodates both discrete and continuous data which is helpful. The analytical algorithms that make up the model are easy to write. The raster model is much faster to use than the vector model. And the raster model is compatible with remotely sensed data
Heads Down Digitizing
Involves standing over a tablet or table and tracing out features manually. This involves both a digitizing table and a stylus or puck with control buttons.
Cartographic scale
Maps can be at a small or large scale. Small scale maps are highly detailed, while large scale maps are more coarse
Ratio Data
Numerical data with a true zero, results can be presented in many different ways
Conical projection
Occurs when you project the geoid onto a cone. This results in the least distortion around mid-latitude areas.
Cylindrical projection
Occurs when you project the geoid onto a cylinder, the cylinder will touch the Earth at its waist (the equator). At this direct contact point there is minimal distortion. As you move away from the point of contact, substantial distortion will occur. This projection is commonly used to demonstrate areas close to and along the equator, where there is low distortion.
Pixels
Pixel is an abbreviation for picture element, or the smallest individual element that make up an image. In raster processing, data is assigned values on a matrix of pixels based on image characteristics or attributes.
Goode's Homolosine Projection
Projection which appears a bit like an orange peel, minimizes distortion - shape and area are preserved more completely than in other equal area projections.
Mercator Projection
Results from a cylindrical projection, results in most distortion around the poles
Map Scale
Scale refers to the relationship or ratio between a distance on a map and the distance on the earth it represents. Maps should display accurate distances and locations and should be in a convenient and usable size
Scanning
Scanning is a digitizing method that converts an analog map into a scanned file. This scan results in raster data. These scans can be collected from rmotely sensed imagery, document imaging and others. When scanning, resolution is controlled by lines or dots per inch being captures. The scanned map datasets don't normally contain spatial reference information, so to use these raster datasets with other spatial data you may need to georeference the new data to a map coordinate system.
Secondary or primary data capture
Secondary or primary data capture. The advantages of secondary data capture include that it is low cost, in that you save both money and time. Additionally, this secondary data can be used to produce digital data based on data from multiple sources (such as paper maps). The disadvantages of secondary data capture include concerns regarding data quality, the inappropriateness of the source data that the secondary data capture is based on.
Examples of georeferencing systems
Street addresses, latitude and longitude, placenames, and GPS
Tangible vs. Mental maps
Tangible maps can be written or drawn, mental maps only exist in the mind of whoever is navigating
GIScience
The body of theory and knowledge that seeks to improve our understanding about the nature of geographic data and how it may be collected, analyzed, and viewed using the logic found within the mapping sciences (i.e., cartography, GIS, surveying, and remote sensing of the environment).
Instruments used in Surveying
The instruments used in surveying include tape measures, range finders and distance measurers (to capture sound, infrared, laser), measuring wheels, levels and transits. In the past, lower-tech instruments such as plane tables and alidades were used.
Remote Sensing
The measurement or acquisition of information of some property of an object or phenomenon by a recording device that is not in physical or intimate contact with the object or phenomenon under study
Vector data model
The vector data model takes an object viewpoint of space, it represents geographic entities as discrete objects composed of points, lines, and polygons. In this model, objects are defined by their x/y coordinates in the planar (Cartesian) coordinate system. Precision in this model is nearly infinite, but accuracy can be limited.
Vector vs Raster - Graphics
The vector model shows real world objects represented as lines, points and areas. Points identify locations and lines connect points while the areas are made up of connected line segments. Raster, on the other hand, uses pixels to denote different data. A grid of rows and columns separates pixels. Since the basic data unit is spatial, x/y coordinates are implicitly. Because of this object information must be explicitly encoded.
GIS Data Representation
This is perhaps the most important feature of GIS and allows us to make a final output which demonstrates the trends or insights that we gained in the data analysis phase. GIS allows you to make maps and other graphics to demonstrate your findings.
Raster Conversion
To convert data for use in GIS you can conduct a raster conversion which involves the scanning of maps, aerial photographs and other documents. It is important to scan based on the spatial and spectral resolution.
Creating and Earth's model Earth ->Geoid ->Ellipsoid process
To create Earth's model, latitude and longitude values are measured on the earth and mathematically leveled to the geoid. From the geoid, points are calculated to corresponding positions on the surface of a spheroid or an ellipsoid.
Topological data model
Topological data models record the x/y coordinates of spatial features and encode spatial relationships between features in the model. In this model, what were ones lines are called arcs and what were once points are called nodes. This model is beneficial because it stores spatial relationships explicitly. This allows us to conduct spatial analysis without having to use coordinates. However, the topological data models does have a more complex data structure which can make it difficult to use. Additionally, topology has to be re-established after each update in the model. Ultimately, this is the preferred system for high-end systems
Georeferencing
a process which involves identifying a series of ground control points that link locations on the raster dataset with locations in the spatially referenced data (target data). The control points are locations that can be accurately identified on the raster dataset and in real-world coordinates. We use these points to shift the raster dataset from its existing location to a spatially correct location.
Example of discrete geographic features
a road, a lake, etc.
Projections
a transformation of the spherical or ellipsoidal earth onto a flat map, these can be onto a flat surface or onto a surface that can be made flat such as a cone or a cylinder. All projections create distortion, there is no perfect projection. These projections can represent the entire earth or just a portion
Raster Analysis
analysis involves mathematical manipulation of the values in the cells of the grid. This analysis can be based on individual or neighborhood cells
What is a map
any concrete or abstract representation of the distributions and features that occur on or near the surface of the earth or other celestial bodies.
Projected coordinate systems
are defined on flat surfaces and are thus 2D. locations are determined by x and y coordinates on a grid, which may not necessarily correspond to the equator and meridians.
Field data capture
collected through GPS and Surveying. GPS is a collection of satellites used to fix locations of Earth's surface. Surveying also occurs in the field. When surveying, the locations of objects are determined by angle and distance measurements from known locations. Surveying is the most accurate method for large scale, small areas.
reference map
contains all information regarding an area in one map
Qualitative maps
contains nominal information such as names or qualities
Primary data capture (direct measurement
data collected in digital format specifically for use in a GIS project. For Raster models, primary data comes in the form of digital remote sensing images and digital aerial photographs. Vector models come into the form of GPS measurements and survey measurements.
Attribute data
data that are linked to the spatial objects to describe properties and characteristics of those objects.
Ordinal data
data that can be placed in a ranking (income, taxable amount, traffic)
temporal data
describes temporal information of spatial objects
Secondary data capture (indirect measurement
digital and analog datasets that were originally captured for another purpose and need to be converted into a suitable digital format for use in a GIS project. These data come in the form of scanning
UTM (Universal Transverse Mercator)
divides the earth into 60 zones at 6-degree intervals. This is used to define horizontal positions worldwide.
Example of continuous. geographic features
elevation, temperature and relative humidity
Spectral resolution
has to do with how many layers or spectral bands are used in the sensor.
Temporal resolution
has to do with how many measurements are taken, over time, in the same place by the same sensor.
Spatial resolution
has to do with how much area is accounted for in each pixel, this resolution can be fine or course.
Radiometric resolution
has to do with the sensor's ability to discriminate very slight differences in energy.
Spaghetti data model
in the spaghetti data model, points, lines, and areas are all encoded in a similar way. Additionally, there is no relationship between points, lines, and areas. This model is simpler to store and understand. Additionally, standard graphic manipulation techniques can be used on closed-loop polygons. Unfortunately, in this model, spatial relationships must be determined for each analysis. It is also true that this model is best for low-end systems.
Nominal data
information that has a name or a layer which can be placed in no hierarchy whatsoever (names, etc) (I.e. counties)
Temporal data
is a special type of attribute. It describes temporal information about spatial objects. It can be thought of as an attribute series over a range of time
Thematic map
isolates one layer or theme of information (I.e. language spoken in the USA, COVID incidence per county)
Example of attribute data
land use categories, vegetation classes, rankings
Examples of spatial data
latitude/longitude, x/y coords, street addresses, administrative units
Types of map scale
map scale can be represented verbally, graphically (using a line to show distance), or as a ratio (1:100,000 or 1/100,000)
Remote sensing data
measurement of objects on Earth's surface using data acquired from aircraft and satellites. This information is collected without physically contacting the object that you are observing. Remote sensing data typically comes from satellites. Spatial resolution and temporal resolution can range substantially based on the satellite used. They also can get remote sensing data from Aerial imagery which can collect data at a local level with a smaller range from 1 meter to several hundreds of meters. Remote sensing data is collected by detecting the energy that is reflected from the Earth. Different materials reflect visible and infrared light in different ways.
Gall-Peters projection controversy
o Peters claimed to have created a new map which accurately represents the developing world. Compared it to the Mercator projection and pointed out the distortion from the Mercator projection. As it would turn out this was a straw man argument because it was well known that the Mercator projection is best used for navigation. Peter's claims sparked controversy because he had not, in fact, designed a new projection. His projection was the exact same as Gall's projection which was published so many years before. Ultimately, Peters used his map to draw attention to a Eurocentric bias which was prevalent in cartographic work. Ultimately, this controversy was more of a struggle between Peters and the cartographic community for authority and respect. The peters projection did ultimately spark a desire for a more accurate representation of the world. And, more broadly, the controversy demonstrated ignorance of cartography amongst the general public.
Continuous geographic features
objects which exist continuously on the landscape. These features are best expressed using a raster model.
Raster attribute data
raster datasets with attribute tables typically have cell values that represent or define a class, group, category or membership
Representative fraction or ratio:
relationship between any unit on a map and the same unit on the ground (I.e. 1: 1,000,000 irl)
Graphical scale
shows directly on the map the corresponding ground distance. Most common on maps because they are easy to understand
Graphical or bar scale
shows the corresponding ground distance directly on the map. These are the most common type of scale shown on maps. They also remain correct even if the map is reduced in size, which makes things easier.
Properties of features
size, distribution, pattern, contiguity, neighborhood, shape, scale, orientation
Second-hand GIS data sources
sources such as rescanned images, digitizing maps, and a digital elevation model. Secondary GIS sources are digital and analog datasets that were originally captured in another format (such as papers or films). These data must be converted either by scanning or digitizing into digital GIS data formats.
4 types of Remote Sensing Resolution
spatial, spectral, temporal and radiometric.
Spatial Resolution
the accuracy associated with the capture of ground information as reproduced in a digital format or graphic display. The finer the resolution, the smaller the cell size, higher spatial accuracy, slower processing and larger the file size.
Raster spatial resolution
the area of a cell equals the spatial resolution
Cartography
the art, science and technology of making maps, together with their study as scientific documents and works of art
GIS Data Management Function
the data base management system performs the input, storage, and retrieval of data that are linked to either vector or raster spatial data.
Heads up Digitizing
the original is scanned and georeferenced, features are captured using the mouse. This involves less fatigue than using a tablet.
Digitizing
the process of converting an analog map or other graphic overlay into digital format with the use of a digitizing table/tablet and manually tracing the input data with a cursor.
GPS Accuracy:
the range of gps is called the pseudo-range because of possible errors. Possible errors can come from the satellite, the GPS signal or the receiver. Satellites can experience error from the clock and also orbital error. The GPS signal could be disrupted by atmospheric and ionospheric delays. And receiver errors could occur due to clock drift and multi-path errors.
Map scale
the relationship or ratio between a distance on a map and the distance on the earth it represents. Maps should display accurate distances and
Geographic scale
the size of the area studied, unit size ranges from global to local. Global view would be the coarsest detail and local view. Would be the finest detail.
Minimum Mapping Unit
the smallest element we can uniquely represent in our data. I.e. the smallest detail we wish to see on our map. The pixel resolution must be half the smallest dimension of the smallest detail we wish to see on our map.
Representative Fraction Scale
the third type of scale is a representative fraction, or ratio scale. Compared to the first two, it is the most abstract but also the most versatile. A representative fraction shows the relationship between one of any unit on the map and one of the same unit on the ground. This is the most versatile scale type because it is not tied to any one unit.
Map elements
title, legend, neatline, scale, orientation (north arrow), and date
Field oriented (model)
treats information as collections of spatial distributions, where each distribution is formalized as a mathematical function from a spatial framework
field oriented (raster)
treats information as collections of spatial distributions, where each distribution is formalized as a mathematical function from a spatial framework.
Object oriented (Data Model)
treats information space as populated by discrete entities that are georeferenced
Object oriented (vector)
treats information space as populated by discrete entities that are georeferenced.
Georgraphic Coordinate Systems
use latitude and longitude. They are 3D and unprojected
Shaded relief map
uses shading to demonstrate topography and other features
Verbal scale
verbal scale expresses in words a relationship between a map distance and a ground distance. i.e. "1 inch equals 16 miles". This type of scale is commonly found on atlases and maps
Geographic information systems
· An information system used to capture, manipulate, summarize, query, edit and visualize spatial and non-spatial information stored in a computer database
Measurements in Georeferencing·
· Georeferences can be metric, nominal, or ordinal. Metric georeferences define location using measures of distances from fixed places. (i.e. distance from the equator or a meridian). Some georeferences are based on ordering such as street addresses and house numbers along streets. Finally, nominal georeferences involve place names which do not have an order or measurement.
Uniqueness in Georeferencing
· Georeferencing data must be unique in that all information is linked to exactly one location. The georeference can be unique within a defined domain, it does not have to be unique globally (for example, there is more than one town named Springfield, but there is only one Springfield, Illinois)
