Straight Line
Allocation and Direction functions
The Straight Line
Allocation function creates a surface where each cell is assigned to the
nearest source based on the straight line distance between them. If there is
only one source, then all of the cells in the surface are allocated to that one
source.
If there is more than one
source, the surface is partitioned into areas of adjacent cells. You can think
of the partitioned areas as compartments dedicated to one feature, such as the
location of a hospital or a store. The size and shape of the compartments is
determined by the proximity of the cells to the sources.
If there is more than one source in a straight line
allocation surface, then cells are assigned to the nearest source. Even if the
distance between a cell and more than one source is the same, the cell is
assigned to only one source.
The cell values in a
straight line direction surface point the way back to the nearest source,
indicating the direction, in degrees azimuth, back to the source. Imagine a
compass, like the one below, hovering over each cell in the surface.
In a straight line direction surface, the cell values are
based on degrees azimuth. With a value of 360, north is the top of the surface.
If there is more than one
source, the cell value is the direction to the nearest source.
In this graphic, source 1 is the nearest source to cell A
and, judging by the angle, is located in a straight line direction of about 15
degrees from cell A. Source 2 lies in a direction of 135 degrees from cell B.
Source 3, 320 degrees from cell C. The source cells, in gray, have a value of
zero, or no direction.