Its area equals the negative sum of all the polygons in the coverage. Also referred to as the external polygon. In tracing, upstream is the direction along the arcs that is against the direction of flow. Direction of flow is determined by a user-defined convention. See directed network .
Elevations are in meters or feet referenced to mean sea level.
Accuracy standards for published maps in English units defining measurements for horizontal and vertical accuracy. A table containing attributes for a grid . In addition to user-defined attributes, the VAT contains the values assigned to cells in the grid and a count of the cells with those values. A coordinate-based data structure commonly used to represent linear geographic features. Each linear feature is represented as an ordered list of vertices .