Available with Spatial Analyst license.
A suitability modeling workflow identifies the best locations to site something or preserve an area. You can use a suitability model to site a housing development, a school, or a corporate headquarters, for example. You can also use a suitability model to identify the best locations to preserve from development for wildlife conservation or fire prevention. Regardless of the potential application, the general workflow is similar.
There are four main steps for creating a suitability model:
- Determine and prepare the criteria data.
- Transform the values of each criterion to a common suitability scale.
- Weight criteria relative to one another and combine them to create a suitability map.
- Locate the areas for the siting or to preserve.
The modeling workflow steps above are used in a sample suitability model described below to identify the best area to preserve for bobcat habitat. The model is for illustrative purpose and does not attempt to define all bobcat interactions. While this example is for identifying bobcat habitat, these general steps can be applied to creating suitability models for many other applications including those mentioned above.
The following image illustrates the sample suitability model workflow:
First, the goal of the suitability model must be articulated. For example, the goal for siting a ski area is not simply to have good terrain and a lot of snow. Instead, the overall goal is the ski area must be financially viable. The terrain and snow attract skiers, allowing the proposed ski area to make money. For the bobcat suitability model, the goal may be to preserve enough habitat area so a stable population of bobcats can be maintained for at least 100 years.
Once the goal is defined, the methods for evaluating the model need to be established. For a ski area, the evaluation method may be measured by the annual profit it would expect to generate. For the bobcat model, it may be to maintain a metapopulation of bobcats that are divided into 6 subpopulations living in 8 connected habitat areas.
Step 1: Determine and prepare the criteria data
The first step to creating a suitability model is to identify the criteria for the subject of the model. In this sample case, this is what the bobcats require for survival. Each criterion identified should be instrumental in reaching the overall goal of the model, which is to ensure a stable bobcat population. The identified criteria should capture the interactions of the bobcats relative to their habitat needs.
In the bobcat example, the following criteria will be considered:
- Slope—Typical bobcat habitat is steep, rugged terrain where they can escape predators.
- Land use types—Bobcats are found in forests and scrubland, not in developed or semideveloped areas.
- Distance from streams—Any preserved locations should be near streams or other water sources.
Since datasets for slope and distance to steams are not initially available, use the appropriate Spatial Analyst tools to derive these criteria from the existing base data. To derive slope, use the Slope tool on the elevation surface. Use the Distance Accumulation tool to determine how far each location is from the closest stream.
Step 2: Transform the values of each criterion to a common suitability scale
Slope, land use, and distance from streams are the criteria that will be used for the suitability model. To proceed, these will be combined. However, mathematically adding the slope, land use, and distance to streams rasters together will result in meaningless values. For example, a location may have a slope value of 5 percent, be 600 meters from a stream, and have a land use of 4, representing single family residential. The resulting sum of these values for the location is 609, an irrelevant number. Before the criteria rasters can be added together, the values within each criterion must be transformed to a common suitability scale.
In this example, a 1 to 10 suitability scale will be used. For each value in a criterion, locations with attributes that are most preferred will receive higher suitability values, while locations with the least preferred features will receive lower suitability values. For example, slopes greater than 25 percent will receive a suitability value of 10, slopes that are between 4 percent and 6 percent will be assigned a suitability value of 5, and slopes that are less than 3 percent will have a suitability value of 1.
When transforming the values within each criterion to the 1 to 10 suitability scale, transform the values relative to one another within the scale. That is, a location assigned a suitability value of 5 is half as preferred as a location assigned a suitability value of 10, and a suitability value of 10 is 10 times as preferred than a location assigned a suitability value of 1.
This transformation process is applied to each value within each criterion identified in the model. For the bobcat model, for the land use criterion, preferred land use types, such as forests, will be assigned a suitability value of 10, residential will be assigned a suitability value of 5, and industry will be assigned a suitability value of 1. For the distance to streams criterion, closer locations will receive a higher suitability value of 9 or 10, and distant locations will receive a lower suitability value of 1 or 2. It is desirable that the assigned suitability values have the same preference between criteria. That is, a slope value that is assigned a suitability value of 5 has the same preference as a land use type or distance to streams location also assigned a suitability value of 5.
The values in each criterion are transformed relative to one another to a common suitability scale. The transformed criteria can now be combined.
Step 3: Weight criteria relative to one another and combine them to create a suitability map
When the three transformed criteria are added together, the resulting range can be from 3 to 30. A location assigned a value of 30 is the most preferred—it would be steep, in forest, and next to a stream. Locations assigned lower values will be less preferred, based on the features located there.
However, before adding the criteria together, it may be that one criterion is more important than the others. If that is the case, that criterion will be weighted more than the others. To emphasize the distinction, the transformation process described in step 2 converts the values within a criterion relative to one another. The weighting in this step defines the relative importance of each criterion to one another.
In the bobcat model, the distance to water criterion has been identified as being 50 percent more important than the slope and land use criteria. As a result, the transformed distance from water criterion values will be weighted (multiplied) by 1.5 before the criteria are added together. The weighting factor for the transformed slope and transformed land use criteria will remain as 1.
Step 4: Locate the areas for the siting or to preserve
A suitability map has been created. Based on the attributes at each location, the suitability map indicates the preference of each location relative to one other from the perspective of a bobcat.
However, bobcats also have spatial requirements. They need a certain amount of area divided between several habitat patches that fall within a specific minimum and maximum size, and the patches cannot be closer together or farther apart than certain distances.
Based on these spatial requirements, the optimal areas will be identified from the suitability map created in step 3.
The patches are located in the most suitable locations of the suitability map (the green areas).
Summary
You learned the following general steps for creating a suitability model:
- Identify the significant criteria.
- Transform the values within each criterion to a common suitability scale.
- Weight the criteria in relative importance to one another and combine them to create the suitability map.
- Determine the best locations from the suitability map based on the defined spatial requirements (in this case, amount of area and number of patches).