GIS Vocabulary
Geodatabase
.gdb or .mdb. Storage file format that can store multiple types of GIS data, including vector, raster, CAD, 3D network, and survey data.
Earth Spheroid/Ellipsoid
A 3-dimension model of the earth capturing its ellipsoidal shape.
Geocoding
A GIS operation for converting street addresses into spatial data that can be displayed as features on a map, usually by referencing address information from a street segment data layer
Attribute Table
A database or tabular file containing information about a set of geographic features, usually arranged so that each row represents a feature and each column represents one feature attribute. In raster datasets, each row corresponds to a certain zone of cells having the same value.
TIGER
A digital spatial database of geographic features, covering the entire United States and its territories, that provides a topological description of these areas.
Census Tract
A geographic region defined for the purpose of taking a census. Generally have a population size between 1200 and 8000 people, with an optimum size of 4000 people. Usually covers a contiguous area, although spatial size varies widely depending on settlement density.
Thematic Map
A map designed to covey information about a single topic or theme, such as population density or geology
Graduated Color Map Symbolism
A map on which a range of colors indicates a progression of numeric values
Graduated Size Map Symbolism
A map on which variation in symbol size is proportional to variation in data values for the attribute that is symbolized
Map Projection System
A method by which the curved surface of the earth is portrayed on a flat surface. This generally requires a systematic mathematical transformation of the earth's graticule of lines of longitude and latitude onto a plane.
Natural Breaks
A method of automatic data classification that seeks to partition data into classes based on natural groups in the data distribution.
Georeferenced scanned map image
A paper map that has been scanned to a digital graphics file and then been aligned to a known coordinate system so it can be viewed, queried, and analyzed with other geographic data
Cadaster
A public record, survey, or map of the value, extent, and ownership of land as a basis of taxation; an official register of the ownership, extent, and value of real property in a given area, used as a basis of taxation
Geographic Coordinate System
A reference system that uses latitude and longitude to define the locations of points on the surface of a sphere or spheroid.
Spatial Feature
A representation of a real-world object on a map
Raster Spatial Data Model
A representation of the world as a surface divided into a regular grid of cells. Useful for storing data that varies continuously, as in an aerial photograph, a satellite image, a surface of chemical concentrations, or an elevation surface.
Vector Spatial Data Model
A representation of the world using points, lines, and polygons. Useful for storing data that has discrete boundaries, such as country borders, land parcels, and streets.
Shapefile
A vector GIS data storage format for storing the location, shape, and attributes of geographic features. Stored in a set of related files that must be located in the same folder.
Georeferencing Spatial Data
Aligning geographic data to a known coordinate system so it can be viewed, queried, and analyzed with other geographic data.
Relational Database Structure
Allow separate data tables (called "flat files") to be linked or combined by matching records having the same values in common fields. Used by ArcGIS.
Boolean Expression
An expression that results in a true or false (logical) condition
Hierarchical Database Structure
Consists of different record types for different information that are linked through "one-to-many" or "parent-child" branching systems that make search and retrieval easy. e.g., Windows Explorer
Equal Interval
Data classification method that divides a set of attribute values into groups that contain an equal range of values
Quantiles
Data classification method that divides the frequency distribution of a variable into equal groups, each containing the same fraction of the total population
Standard Deviation
Data classification method that finds the mean values, then places class breaks above and below the mean at intervals of standard deviations until all the data values are contained within the classes. Values 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
Interval Scale Data
Data classified on a linear calibrated scale, but not relative to a true zero point in time or space. Because there is no true zero point, relative comparisons can be made between the measurements, but ratio and proportion determinations are not as useful
Ratio Scale Data
Data classified relative to a fixed zero point on a linear scale
Ordinal Scale Data
Data that can be rank ordered (1st, 2nd, 3rd, etc.) by which data can be sorted, but still does not allow for relative degree of difference between them
Unprojected GIS Data
Digital spatial data that has not been projected through a map projection system. It may have a 3-dimensional Geographic Coordinate System (GCS), but may not have been projected into 2 dimensions.
Land Use/Land Cover (LULC) GIS Data
Digital spatial thematic data- typically in either vector or raster format- that maps the types of basic physical land cover or that maps how the land is being used by humans
Population projection
Estimate of the population for future dates. Illustrate possible courses of population change based on assumptions about future births, deaths, net international migration, and domestic migration.
Location Identifier Attributes
FID, OID, or OBJECTID; Unique identifiers in the GIS attribute table automatically created by ArcGIS to give every feature a unique numeric ID
Project File (.mxd)
File format in which the maps created from ArcGIS can be stored. Also stores map symbology, layout, hyperlinks, toolbars, etc. Does not save actual GIS data
Small Scale
Generally, a map scale that shows a relatively large area on the ground
Large Scale
Generally, a map scale that shows a small area on the ground at a high level of detail
Dissolve
Geoprocessing command that spatially merges features that have the same value for a particular class, removing unnecessary boundaries between polygon features or unnecessary vertices between line features
Layer File (.lyr)
In ArcGIS, a GIS layer with this extension stores the path to a source dataset and other layer properties, including symbology. Does not save actual GIS data.
Layer
In ArcGIS, a reference to an individual spatial data source, such as a shapefile, coverage, geodatabase feature class, or raster
Snapping Tolerance
In an ArcGIS editing session, the distance within which the pointer or a feature will snap to another location.
Map Projection On the Fly
In the ArcGIS software, ArcMap can display data stored in one projection as if it were in another projection. The new projection is used for display and query purposes only. The actual data is not altered.
Datum
In the context of georeferencing systems, this defines the origin and orientation of a Geographic Coordinate System (GCS). There are hundreds in use around the world, including the frequently-used WGS84 and NAD83.
Degrees, Minutes, Seconds
In the so-called "Geographic" version of Geographic Coordinate System (GCS), these are units of angular measure (60 of the smaller unit = 1 of the next larger unit)
Metadata
Information that describes the content, quality, condition, origin, and other characteristics of data or other pieces of information. May describe and document subject matter; how, when, where, and by whom data was collected; availability and distribution information; its projection, scale, resolution, and accuracy; and its reliability with regard to some standard.
Random Spatial Sampling
Locations obtained by choosing x-coordinates and y-coordinates at random within the spatial area being sampled
Cadastral map
Map that shows the boundaries and ownership of land parcels
Nominal Scale Data
Noncomparative, descriptive scaled data; Data divided into classes within which all elements are assumed to be equal to each other, and in which no class comes before another in sequence or importance.
Attribute
Nonspatial information about a geographic feature in a GIS, usually stored in a table and linked to the feature by a unique identifier.
Remote Sensing Imagery
Spatial data acquired from satellites and aircraft
Systematic Spatial Sampling
Spatial sampling based on a specific systematic pattern, such as points or transects regularly spaced, across the area being sampled. The location of the first point or transect is selected randomly.
Base Map
The base GIS layer maps that provide a framework for a GIS analysis project
Spatial or Geostatistical Interpolation
The estimation of surface values at unsampled points based on known values of surrounding points. Techniques included Inverse Distance Weighted, spline, and kriging.
State Plane Coordinate System
The most widely used coordinate information in local and regional surveying and mapping applications in the United States and its territories. Coordinate system that divides the 50 states of the United States, Puerto Rico, and the U.S. Virgin Islands into more than 120 numbered sections, referred to as zones. Each zone has an assigned code number that defines the projection parameters for the region, with each zone having its own projection.
Spatial resolution
The pixel size of a digital airphoto or satellite sensor image, corresponding to a specific size of surface area being measured on the Earth's surface
Stratified Spatial Sampling
The process of dividing members of the geographic area to be sampled into homogeneous spatial subgroups before sampling. Then simple random spatial sampling or systematic spatial sampling is applied within each stratum. This often improves the representativeness of the sample by reducing sampling error. It can produce a weighted mean that has less variability than the arithmetic mean of a simple random sample of the population.
Map Scale
The ratio of a distance on a map to the equivalent distance measured in the same units on the ground.
Digital Elevation Model (DEM)
The representation of continuous elevation values over a topographic surface by a regular array of z-values. Typically used to represent terrain relief.
Cartography
The science and art of making maps
High Accuracy Reference Network (HARN)
The statewide or regional upgrade in accuracy of North American 1983 Datum (NAD83) coordinates using Global Positioning System (GPS) observations that was completed in the 1980s and 1990s. With observed to support the use of GPS by federal, state, and local surveyors, geodesists, and many other applications, with very high horizontal accuracy
Public Land Survey System
The surveying method used historically over the largest fraction of the United States to survey and spatially identify land parcels before designation of eventual ownership
Decimal Degrees
Values of latitude and longitude expressed in decimal format rather than in degree, minutes, and seconds.
