Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition

Vector Data Model

Using the vector approach, the level of difficulty of determining “what” and “where” is somewhat reversed. The “what” is relatively simple. Each unique area is enclosed inside a polygon, so the content of the polygon is homogeneous—containing a unique value (or a unique set of values) related to the theme. Contrast this with the raster approach, where several features or conditions may occur in one cell and (usually) one feature or condition is picked for recording in the database.

The “where” with the vector approach is a bit more problematical but usually allows greater precision. Whereas with a raster approach, the location of each area (cell) is but a simple calculation, with the vector approach, each vertex of each polygon has an explicit geographic location. Therefore, the “where” question may have thousands to millions of answers, in terms of coordinate pairs for a large area or one with many polygons that have complex boundaries. Of course, the issue with respect to projection, datum, and so on are present—for all the coordinate pairs.