| # GRASS Help System

arc - GRASS vector maps are stored in an arc-node representation consisting of non-intersecting curves called arcs. An arc (a.k.a., vector) is stored as a series of x,y coordinate pairs. The two end-points of an arc are called nodes. Two consecutive x,y pairs define an arc segment (a.k.a., line segment). Arcs, either singly or in combination with other arcs, form higher-level map features: line features (e.g., roads or streams) and area features (e.g., soil types or timber cutting units). Areas are also called polygons. GRASS vector format does not store the polygons explicitly; they are reconstructed by finding the particular arcs which form the polygon perimeter. Arcs that form linear features are sometimes called lines and arcs that outline areas are called area edges or area lines.

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Automatically created on: Sun Apr 10 10:50:17 2005