# Tracking Creatures of Bavarian Folklore Using a Least-Cost Path Model

Table of Contents

## Creating Cost Surface Models Using a Relative Cost Scale

A cost surface model represents some factor or a combination of factors that affect travel across an area. The goal is often to find the path with the least cost. In this scenario, the following cost factors have been identified:

• Elevation
• Slope
• Tree canopy density
• Hydrology

Since there are multiple cost factors in this analysis, your goal is to create a total cost surface model. A total cost surface model is used when you have multiple cost factors that you wish to combine into a single cost surface model. When you need to consider multiple cost factors, uniform cost units must be used. The values of the cost units must be converted into a relative cost scale, which is a universal scale that represents the costs between different cost factors. A relative cost scale could be as simple as a scale of 1 through 10. The number 1 might represent a low cost or low high likelihood of travel. The number 10 might represent a high cost or even a prohibitive factor. For the results to be meaningful, the relative scale must be the same among the different cost factors.  Each cost category must be given the same relative scale, where the numbers roughly represent the same level of difficulty or likelihood of travel. In this example, you want to create a total cost surface to use for modeling the wolpertinger migration from den locations to the town of Orick. The problem is that each of the cost factors currently uses different units. Elevation uses meters, slope uses degrees, and tree canopy uses density, etc. To solve this, you will reclassify each of these layers to create a relative cost scale. Though the relative scale is unitless, the values between the cost factors are meaningful when compared to each other. Typically, developing the relative scale between cost factors would involve extensive research. In this scenario, we will assume thorough research was conducted by the HSU students. Once each of the cost factors is reclassified into relative units, they can be combined to create a total cost surface model. The table below defines the relative cost for each cost factor. In later steps, you will use the Reclassify tool to create new layers with relative cost values.

 RelativeCost Elevation Slope TreeCanopy WaterFeatures 1 >1000 >35 >90 No water 2 >800 to 1000 >30 to 35 >80 to 90 3 >600 to 800 >60 to 80 4 >400 to 600 >25 to 30 5 >200 to 400 >40 to 60 6 >100 to 200 >20 to 25 7 >1 to 100 >20 to 40 8 >10 to 20 9 >5 to 10 10 >-1 to 1 0 to 5 0 to 20 Water