A coverage is a collection of feature classes used to represent geographic phenomena. Each coverage is a directory stored as a series of files.
The set of features contained in a coverage depends on the type of geographic phenomena being modeled. The following table gives a brief description of the types of phenomena each feature class is used to model:
Coverage feature classes
| Feature class | Application and use | Examples |
|---|---|---|
Point | Point locations | Well sites, mountain peaks |
Arc | Linear features | Street sections, contours, streams, sewers, power lines, gas lines |
Node | Connecting points and endpoints of linear features | Valves on pipelines, intersections of streets, power poles, manhole covers |
Route | Linear features | Streets, contours, stream networks, sewers, power line networks, gas line networks, street addresses |
Section | Defines route features | Street section, traffic lanes, pipe condition, above- and below-ground transmission lines |
Polygon | Area features | Soil units, land use, parcels, building footprints, forest stands, ownership |
Region | Area features, multiple polygons | Census geography, state of Hawaii, overlapping wildlife habitat |
Annotation | Feature labels | Street names, place-names on road maps |
Tic | Geographic registration and control | Registration for digitizing |
Link | Rubber sheeting and adjustment | Edgematching map sheets, feature snapping, datum adjustments |
Coverage extent | Defines map extent | Rectangle describing outer boundary of coverage |
Coverage feature class file description
| Feature class | Description | Attribute table name: <cover>.* |
|---|---|---|
Point | A point defined by an x,y coordinate pair used to represent point features or assign User-IDs to polygons. | pat.adf |
Arc | A line defined as a set of ordered x,y coordinates used to represent linear features and polygon boundaries. | aat.adf |
Node | The endpoints of an arc or the point at which two or more arcs connect. | nat.adf |
Route | A linear feature composed of one or more arcs or parts of arcs. | <route>.rat |
Section | An arc or portion of an arc used to define a route or the building blocks of routes. | <route>.sec |
Polygon | An area defined by the arcs that make up its boundary, including arcs defining any islands inside. User-IDs are assigned to label points. | pat.adf |
Region | A collection of one or more contiguous or noncontiguous polygons defining a geographic feature. | <region>.pat |
Annotation | A text string describing a geographic feature. Shape points are used to position and draw annotation. | <anno>.tat |
Tic | A geographic reference or control point used to register and transform the coordinates in a coverage. | tic.adf |