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GIS Chapter 1 Vocab
Introduction to Geographic Information Systems
| Term | Definition |
|---|---|
| discrete | data that take on a relatively small number of distinct values. |
| continuous | data that take on a variety of values and that change rapidly across a data set, such as elevation. |
| vector | a spatial data storage method in which features are represented by one or more pairs of x-y coordinate values forming points, lines, or polygons. |
| raster | a data set composed of an array of numeric values, each of which represents a condition in a square element of ground. |
| georeferenced | a spatial data layer that is tied to a specific location on the earth's surface for display with other data. |
| coordinate system | (1) a specified range of x-y values onto which a map is plotted; (2) the definition of a coordinate space used by a map layer, including the ellipsoid, datum, and projection. |
| features | a spatial object composed of one or more x-y coordinate pairs and having one or more attributes in a single record of an associated table. |
| point | a one-dimensional feature defined by a single x-y coordinate pair. |
| line | a spatial feature composed of a string of x-y coordinate vertices and used to represent linear features such as streets. |
| polygons | a closed, two-dimensional area feature defined by three or more x-y coordinate pairs. |
| nodes | the beginning and endpoint of a line feature. |
| vertex | a point at which the segments of a line or polygon feature change direction |
| vertices | Plural of vertex. |
| feature classes | a set of similar objects with the same attributes stored together in a spatial data file. |
| Feature ID (FID) | a unique number assigned to every feature in a spatial data file and used for identification and tracking. |
| ObjectID (OID) | unique number identifying a row in a table or a feature in a geodatabase feature class. |
| thematic mapping | displaying the features of a spatial data layer based on values in its attribute table. |
| feature datasets | a set of feature classes in a geodatabase that share a common coordinate system and can participate in networks and topology. |
| spaghetti model | a model that stores spatial features as a series of x-y coordinates and does not store topological relationships between features. |
| topological model | a data model that stores spatial relationships between features in addition to their x-y coordinates. |
| topology | the spatial relationships between features, such as which are connected or adjacent to each other. |
| adjacency | a spatial condition that quantifies whether one feature touches another. |
| connectivity | a property of linear features when they are connected to each other via junctions. |
| overlap | a spatial condition that quantifies whether one feature covers all or part of another feature. |
| intersection | the property of two features touching each other in whole or in part. |
| logical consistency | a measure of how well data features represent real-world features, in particular with respect to topology. |
| cells / pixels | a square data element in a raster corresponding to one value representing conditions on the ground. |
| digital elevation model (DEM) | a raster array of values representing elevations a the earth's surface. |
| digital raster graphic (DRG) | a scanned image of a USGS topographic map. |
| geographic coordinate system (GCS) | a spherical coordinate system of degrees of latitude and longitude that is used to locate features on the earth's surface. |
| map units | the units of the coordinate system in which a map is stored or displayed. |
| map scale | the ratio of feature size on a map to its size on the ground. |
| source scale | the original analog scale or resolution at which a digital data set is converted to digital form. |
| generalization | simplifying a feature in order to store it or display it at smaller scales than its source scale. |
| geometric accuracy | the accuracy with which the shape and position of features are represented. |
| thematic accuracy | the degree to which attribute values represent the true properties in the real world. |
| resolution | (1) the ground area represented by one cell value in a raster; (2) the default storage precision of a vector data set. |
| precision | the number of digits allotted to store a numeric value. |
| metadata | information stored about data to document its source, history, management, uses, and more. |
| coverage | the spatial data format created for, and used by, ArcInfo. |
| shapefile | the spatial data model developed for, and used by, ArcView 3 and later versions. |
| map documents | file used by ArcMap to contain a set of data for mapping and analysis. |
| layout | the specification for a map page, including the map frames, legend title, scale bar, and so on; stored in a map document. |
| layer | a reference to a feature class and its associated properties. |
| layer properties | settings that control how a data set is to be displayed or viewed in ArcMap. |
| layer file | a file that stores a pointer to spatial data along with information on how to display it. |
| active frame | the data frame that is visible and responds to changes by the user. |
| TINs | (Triangulated irregular network) a data model for storing surfaces as triangular facets with varying orientations. |
| dBase | a database program whose file format has been adopted for the shapefile data model and tables in ArcGIS. |
| multipart features | a single feature composed of nontouching units, such as a single state feature composed of the seven Hawaiian islands. |
| map service | an Internet map that is available for viewing but that cannot be manipulated, symbolized, or saved by the user. |
| feature service | an Internet map layer in which the actual features are available for display, query, and sometimes editing. |
| layer package | a file sent from a GIS sever with the symbol properties and necessary data included for use. |
| map package | a file sent from a GIS server with the map layout and necessary data included for use. |
| image service | an Internet GIS service that provides imagery for display or analysis. |
| geoprocesssing service | an analysis tool provided by a GIS server, in which the processing is done on the server rather than on the client's device. |
| cloud | a computing system composed of warehouses of computers and hard drives managed by a company that rents processing power and disk space to clients. |
| web map | an interactive map based solely on Internet data services and accessed from many platforms, including desktop software, web pages, and mobile devices. |
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