The Cost Weighted
Distance function
Distance and direction
surfaces created with the Cost Weighted Distance function are used in a
least-cost path analysis. With the exception of the cost weighted allocation
surfaces, cost weighted surfaces are normally not used directly in analysis;
whereas straight line distance surfaces often are.
Cost weighted surfaces are
generally not used directly in analysis because cell values in a cost weighted
distance surface are not distance values, but accumulated costs.
To calculate the cell
values in a cost weighted surface, the Cost Weighted Distance function
evaluates the neighbors of each cell, beginning with the source, multiplies the
average cost between each pair by the distance between them, and assigns each
of the neighboring cells a cost weighted value. The process moves to the cell
with the lowest value, evaluates its neighbors with unknown values, and so on.
This graphic illustrates the iterative process behind the
Cost Weighted Distance function.
Instead of a compass
direction, each cell value in a cost weighted direction surface is given a code
number that indicates the direction of the next least-cost cell. The decoder
diagram below shows the direction each number code points.
If a cell has the code value of 5, the next least cost
cell back to the source is to the left. If the code value is 8, the next least
cost cell back to the source is to the upper right.
In an allocation surface
created with the Cost Weighted Distance function, the shape and size of its
compartments are determined by the cost of travel from the cells within it to
the nearest source. This type of analysis would be useful if you had to
consider the size of service areas based on the cost of travel over land.