Structures for Storing Geographic Data - Introducing Geographic Information Systems with ArcGIS - page 231

FIGURE 4-2 An orthophotoquadrangle of part of Lexington, Kentucky

❏ WHAT? (entity or quantity)

❏ WHERE?

I don't know how you would do this. If you think about it, you may come up with a viable, effective, and
efficient scheme that no one else has thought of. If so, head for the patent office.

Here are approaches that others have come up with:

❏ Systematically divide the overall area up in a regular way into a large number of equally sized

subareas (e.g., small squares). Record what is in each subarea. Have a reference scheme so that you
know where each subarea is. This technique falls under a broad category called raster (or grid or cell ).
Almost always, a raster may be viewed as a rectangular space composed of rows and columns.
A given cell is at the intersection of a given row and a given column.

❏ Completely delineate each of the features—“delineate,” in this case, is a real, physical de line ation.

It means: in the two-dimensional plane, draw a series of straight-line segments around each area.
Develop a method for determining where the lines are and for giving each segment a direction. This
is often referred to as a vector 2 approach, since a directed straight-line segment is a vector.