Coverages

(Getting Started with ArcGIS starting on p. 50)

Coverages contain primary, composite and secondary feature types.

Primary features in coverages are

• label points,
• arcs, and
• polygons.

Composite features are built from primary features.

Secondary features are

• tics,
• links,
• annotations which are used to provide text about the geographic features on the maps.

Primary Features

Label points can represent individual point features (e.g. wells, intersections etc). The points label or link the attributes to polygons. Each polygon in a coverage has a single label point with its feature ID number, usually at the center.

Arcs are connected sets of line segments, with nodes at the endpoints. Arcs can be organized into polygons that represent areas.

Nodes are the endpoints or and connections between arcs. Nodes can have attributes so that they can represent point features in a network such as values in a network of water mains. Nodes are important because they connect "features" to each other. (form the topology???) Although Nodes are not technically listed as features they act like a primary feature - essentially a label point. Not every conjunction between two lines is a node. An arc may be made up of several line segments, but only the ends are nodes.

Polygons represent areas bounded by arcs, including island polygons. We DEFINE polygons such that they do NOT OVERLAP. a point can fall into at most one polygon.