# Cost Path Analysis This map shows the results of a spatial model to calculate the least cost path between a stand of forest being cut and the nearest sawmill.
Cost path analysis is a procedure or tool in Geographic information systems for finding an optimal route between two points through continuous space that minimizes costs. "Cost" in this sense can have a number of connotations, including: actual monetary expenditure in construction, time and effort required to travel, and negative environmental impacts. Any path through space will accumulate these costs, and routes with high associated costs are less favorable than routes with a lower cost associated with it. Cost path algorithms are designed to efficiently find the path with the minimum total cost.

Cost Path is one of a series of algorithms and tools that analyze such costs, collectively known as Cost Distance Analysis. Its most common application is for planning corridors for constructing linear infrastructure such as roads and utilities.

# Analysis Procedure

Determining an optimal cost path typically requires three steps, which in most GIS software is implemented in separate tools (because they can be used in other procedures).

### 1. Cost Surface

The various types of cost are combined into one comprehensive measure that could be measured anywhere in the space (thus creating a field), then modeled in GIS (typically with an Index model procedure) to create a raster grid known as a cost surface.

### 2. Cost Distance

Given a source location, a new raster grid called a cost distance raster is created that calculates the accumulated cost to travel to each cell from the source. This is created by radiating out from the source, determining the cost of each cell by identifying the neighbor with the lowest accumulated cost and adding its cost to the total. Simultaneously, a separate grid, called a backlink raster encoding the direction from each cell to its lowest cost neighbor.

### 3. Least-cost Path

Given a destination location, this algorithm finds the corresponding cell in the backlink raster, then traces a path from the destination back to the source by following the direction of each cell to the lowest cost neighbor. The corresponding cell in the cost distance raster gives the total cost accumulated by following this optimal route.