area A closed figure (polygon) bounded by one or more arc features that enclose a homogeneous area.
attribute A characteristic of a map feature described by numbers or characters, typically stored in tabular format, and linked to the feature by a user-assigned identifier.
CAD Computer-Aided Design. An automated system for the design, drafting and display of graphically oriented information.
clip The process of extracting data from a coverage that reside enitirely within the boundary of features in another coverage (called the clip coverage)--much like a ‘cookie-cutter'.
coordinate An x,y location in a Cartesian coordinate system or x,y,z in a three-dimensional coordinate system. Coordinates are used to represent locations on the earth's surface relative to other locations.
coverage A digital analog of a single map sheet forming the basic units of data storage in ARC/INFO. In a coverage map features are stored as primary features, such as arcs, nodes, polygons, and label points, and secondary features, such as tics, extent and annotation. A coverage usually represents a single theme or layer, such as soils, streams, roads, and land use.
database A logical collection of files managed as a unit
digitizer A device consisiting of a table and a cursor with crosshairs and keys used to record the location of map features as x,y Cartesian coordinates. Also refers to the title of the person using the device to automate coverages.
digitizing The process of using a digitizer to automate the locations of geographic features by converting their position on a map to a series of x,y Cartesian coordinates stored in computer files.
DLG Digital Line Graph files from the U.S. Geological Survey. These files include digital information from the USGS map base categories, such as transportation, hydrogaphy, contours, and public land survey boundaries.
geographic data The locations and descriptions of geographic features. The composite of spatial data and descriptive data.
GIS Geographic Information System. An organized collection of computer hardware, software, geographic data, and personnel designed to efficiently capture, store, update, manipulate, analyze, and display all forms of geographically referenced information. Certain complex operations are possible with a GIS that would be very difficult, time consuming, or otherwise impracticable.
RMS error The root mean square (RMS) error represents the amount of error between original and new coordinate coordinate locations. The lower the RMS error, the more accurate the digitizing or transformation.
Topology The spatial relationships between connecting or adjacent coverage features (e.g. arcs, nodes, polygons, and points). Topological relationships are created from simple elements or dimensions into complex ones. Points (1 dimension) are the simplest element. Points form arcs or lines (2 dimension) and arcs form the boundary of a polygon, (3 dimension = area). The topology of an arc, for example, are its from- and to-nodes and, if it forms a polygon, its right and left polygon.