Spatial Analysis Based on Raster Data Processing - Introducing Geographic Information Systems with ArcGIS - page 469

A Source grid
A Cost Distance grid
A Cost grid
FIGURE 8-15 Making a cost distance raster
cell (dark) and every other cell. 7 Notice particularly the northwest and southeast corners of the resulting
raster. Even though they are the same distance from the source cell, it is clear that it is more expensive to
travel from the northwest than from the southeast. The reason is that southern cells are cheaper to cross
than northern ones.
When you apply the Cost Distance tool, the resulting raster shows up in ArcMap (asuming it is running)
as a raster that you provide a name for.
Path Calculation in Euclidean Distance and Cost
Distance
It is worth mentioning that the straight-line distance from a given cell produced by Euclidean distance
compared with the least-cost path generated by cost distance are quite different; they are calculated
in completely different ways. Euclidean distance calculates the direct, straight-line distance from each
cell center to the closest source cell center, regardless of how this path slices through intervening cells.
The cost distance path, however, must pass through cell centers, frequently generating a sequence of line
segments that change direction at the center of each cell.
Therefore, even when crossing a cost surface where each cell cost is 1, so that a straight line would be the
least-cost path, cost distance will usually produce a slightly longer path—because the path proceeds from
cell center to adjacent cell center. This sort of “connect the dots” behavior will not result in a much longer
path than the straight-line distance, but observing it illustrates the difference in the ways the two output
7 A calculation is made for every cell in the raster.