# Creating a least cost corridor

Available with Spatial Analyst license.

## What is a corridor?

The Corridor tool returns a raster in which, for each cell location, the sum of the cost distances (accumulative costs) for two input accumulative cost rasters is calculated. The sum of the two raster costs identifies for each cell location the least-cost path from one source to another source that passes through the cell location.

The Corridor tool is related to the Cost Path tool, which only returns an output raster with the least-cost paths.

## Why find the least-cost corridor?

You could use the Corridor tool instead of the Cost Path tool to connect two patches of deer habitat in a conservation plan and want to conserve the optimal corridor for the deer instead of just buffering a single path.

## Creating a corridor

To create a corridor, two cost accumulative rasters must be created using a cost distance tool (Cost Distance or Path Distance, for example), one for each source (or set of sources). The diagrams below show the cost surfaces being created from a single cell location for demonstration purposes. The procedure actually occurs for each cell location on the input rasters.

The Corridor tool then adds the two accumulative cost surfaces together.

The output raster does not identify a single least-cost path between the two sources but identifies the range of accumulative costs between the sources. That is, the least accumulative cost to reach source 1 plus the least accumulative cost to reach source 2 equals the total accumulative cost of a path passing through a cell. It is the least accumulative cost if a path is routed through the cell from source 1 to source 2.

If all cells with values less than a maximum accumulated distance (or threshold) are selected from the corridor raster, the resulting output raster will correspond to a swath (or corridor) of cells that do not exceed a specified cost. The resultant threshold output can be viewed as the least-cost corridor of cells, not the least-cost path (a single line).

## Alternative methods

Another way to limit the corridor to a specified threshold is through a conditional instruction. Several examples of implementing this with different tools follow.

• Using the Con tool (from the Conditional toolset) with the following settings:

Input conditional raster : accum_cor

Expression : "Value < 100"

Input true raster or constant value : 100

Input false raster or constant value : 0

Output raster : corr_thresh

• Using the Extract By Attributes tool (from the Extraction toolset) with the following settings:

Input raster : accum_cor

Where clause : "Value < 100"

Output raster : corr_thresh

• Using the Test tool (from the Math > Logical toolset) with the following settings:

Input raster : accum_cor

Where clause : "Value < 100"

Output raster : corr_thresh

If multiple sources were input to the cost distance tool to create the input accumulative cost rasters to the Corridor tool, then depending on the accumulative cost values between sources and the threshold specified, multiple corridors might result (one between each of the sources).