GIS

Terms

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Ratio
Data with known intervals between values that are based on a meaningful zero value, Population densities
Choropleth
A map that applies shading symbols to data or statistics collected for enumeration units such as counties or states
Azimuthal
Retains certain accurate directions, Uses a plane as the projection surface
Sources of spatial data
Existing: Federal, State, Local, Commercial. Create it yourself
Suitability analysis
Analyzing an area to see whether it is good to do whatever you want to do there
Marginalia
Title, Legend, Scale, Compass, Explanations
Sources of uncertainty/error
Spatial and informational, Derived sources (maps, secondary?), Measuring device, Bias/subjectivity, Sampling, Spatial autocorrelation (like values spatially close to each other), Interpolation (estimation)
Datum
Point of reference used to measure locations on the surface of the earth, Defines the origin and orientation of the lines of latitude and longitude, Always related to a spheroid
Normalization
The process of taking a table with all the attribute data and breaking it down to small tables while maintaining the necessary linkages between them in a relational database
Equidistant
Maintains consistency of scale for certain distances
Decision support
A computer program that includes data presentation and modeling tools that help people understand problems and find solutions
Interval
Data with known intervals between values, Temperature readings
Components of GIS
Hardware, Software, People, Data and Infrastructure
Conformal
Preserves local shapes
Equivalent
Represents areas in correct relative size
Cylindrical
Uses a cylinder as the projection surface
Service Area
Type of network analysis for determining the region that encompasses all streets that lie within a specified impedance, For example, the 20-minute service area for a fire station includes all the streets that can be reached within 20 minutes from that location.
State Plane Coordinate System
A coordinate system developed in the 1930s to permanently record original land survey monument locations in the United States. Most states have more than one zone based on the SPC27 or SPC83 system
Nominal
Data that shows different kinds or different categories, Land-use types or soil types
Raster data model
A spatial data model that uses a grid and cells to represent the spatial variation of a feature, Represent continuous features, Simple data structure with rows and columns and fixed cell locations
Layout
The arrangement and composition of various map elements, Focus, order and balance
Visual Hierarchy
The process of developing a visual plan to introduce the 3-D effect or depth to maps, Placing elements at different visual levels according to their importance to the map's purpose
Dasymetric
A map that uses statistics and additional information to delineate areas of homogenous values, rather than following administrative boundaries
Buffer
A GIS operation that creates zones consisting of areas within a specified distance of select features
Other Considerations in Making a Map
Purpose, Audience
Polygon overlay
A GIS operation that combines the geometries and attributes of the input layers to create the output
Projected Coordinate System
A plane coordinate system that is based on a map projection
Ordinal
Data that are ranked, Large, medium and small cities
Geographic Coordinate System
A location reference system for spatial features on the Earth's surface, Defined by longitude and latitude
Descriptive models
A model that describes the existing conditions of spatial data
Earth-centered
1983 North American Datum (NAD83): The origin is very close to the earth's center of mass, Most commonly used datum for North America
Isarithmic
A map that uses a system of isolines to represent a surface
Methods of data entry
Convert data, Create data: Scanning existing maps, Digitizing, Tablet, Heads-up (softcopy), Image Processing, GPS, Surveying, Geocoding
Model
A simplified representation of a phenomenon or a system
Lambert conformal conic
A common map projection, Basis for the State Plane Coordinate system for many states
Natural breaks
A method of manual data classification that seeks to partition data into classes based on natural groups in the data distribution, Occur in the histogram at the low points of valleys, Breaks are assigned in the order of the size of the valleys, with the largest valley being assigned the first natural break
Polygon-on-polygon overlay
A GIS operation in which the output combines the polygon boundaries from the inputs to create a new set of polygons and each new polygon carries attributes from the inputs
Standard deviation
A data classification method that finds the mean value, then places class breaks above and below the mean at intervals, Values that are beyond three standard deviations from the mean are aggregated into two classes, greater than three standard deviations above the mean and less than three standard deviations below the mean
Shortest path
A network analysis approach that finds the path with the minimum cumulative impedance between nodes on a network
Boolean
A keyword such as AND, OR, XOR, or NOT that is used to construct compound expressions
Vector data model
A spatial data model that uses points and their x-,y-coordinates to construct spatial features of points, lines and areas, Ideal for representing discrete features: Points, Lines, Areas. May be georelational or object-based, May or may not involve topology, Nay include simple or composite features
Equal interval
A data classification method that divides a set of attribute values into groups that contain an equal range of values
Histogram
Bar chart that groups data into equal intervals, Uses bars to show the number or frequency of values falling within each class
Quantile
A data classification method that distributes a set of values into groups that contain an equal number of values
Point-in-polygon overlay
A GIS operation in which each point of a point layer is assigned the attribute data of the polygon within which it falls
DEM
A digital model with an array of uniformly spaced elevation data in raster format
Transverse Mercator
A common map projection, Basis for the Universal Transverse Mercator grid system and the State Plane Coordinate system, Central meridian is 90°W and the latitude of true scale is the equator
Prescriptive models
A model that offers a prediction of what the conditions of spatial data could be or should be
Local
Aligned so that it closely corresponds to the earth's surface for a particular area, 1927 North American Datum (NAD27): Uses Meades Ranch, Kansas as the point of origin for all measurements
Location/Allocation analysis
Solves problems of matching the supply and demand by using sets of objectives and constraints