Combine rasters for spatial decision making with the new Multicriteria Overlay tool
Multicriteria Decision Analysis (MCDA) is a structured approach in spatial decision-making that involves two steps: first, transform all criteria onto a common scale; second, weight and combine those transformed criteria to produce a final output. In ArcGIS Pro, Weighted Sum and Weighted Overlay have long been the most widely used methods for the second step. Both of these methods assume that a higher suitability value from one criterion can compensate for lower values from another criterion. However, many real-world problems require more specialized overlay approaches: some need a method that penalizes locations if even one criterion is much less than the others, while others may call for finding locations that are simultaneously closest to ideal but farthest from undesirable conditions. To address this gap, the new Multicriteria Overlay geoprocessing tool brings seven overlay methods together in one tool.
Before running the tool, prepare your input rasters so they share a common evaluation or suitability scale, such as 1 to 10 or 0 to 1. You can use the Rescale by Function or Reclassify geoprocessing tools to perform this transformation. Once your rasters are on a common scale, in the Multicriteria Overlay tool choose the Overlay Method that best matches your analytical goals, then assign the relative weights reflecting the importance of each criterion, and run the tool.
The output is a floating-point raster in which each cell value represents the combined evaluation or suitability score derived from all input criteria using the selected method.
Note: The Ideal point solution (TOPSIS) method does not need the criteria to be transformed. Instead, it standardizes each input raster internally, so your inputs can remain in their original units.
How to choose an overlay method
Choosing the right overlay method is one of the most important decisions in a multicriteria analysis. The table below provides a comparison followed by real-world application examples.
| Method | Best Used When | Example Applications |
| Weighted sum | Tradeoffs are acceptable; high values can offset low values | Wind farm sitting, vineyard plantation planning |
| Weighted geometric mean | Low values in any criterion should reduce overall suitability | Habitat suitability index, aquaculture site evaluation |
| Maximum | A single strong criterion is enough to qualify a location | Mineral prospectivity mapping, wireless coverage planning |
| Minimum | A single weak criterion should disqualify a location | In a dry area, water might be a limiting-factor in a habitat model. For a solar farm sitting solar potential might be a limiting-factor |
| Weighted overlay | Criteria influence should be expressed as percentages summing to 100 and output values need to be rescaled to a specified range. Tradeoffs are acceptable. | Site suitability scoring with defined contribution per criterion |
| Ordered weighted averaging | Explore best-case, worst-case, and balanced scenarios by adjusting how much influence the highest or lowest ranked criteria have on the result | Agricultural planning, landslide susceptibility mapping |
| Ideal point solution (TOPSIS) | A location's suitability is determined by how close it is to ideal conditions and how far it is from the least desirable conditions | Sustainable urban development, solid waste site selection |
Compare Methods
The choice of Overlay Method can significantly influence which locations are identified as most suitable. You can compare the outputs visually or analytically to distinguish differences among the methods, particularly exploring the spatial distribution of the highly suitable areas with the less suitable areas. To further analyze and quantify these differences, run the Multicriteria Overlay tool with multiple methods, followed by applying the Locate Regions to each output. This will provide you with a powerful way to reveal how candidate sites change under different overlay assumptions.
In a winery site selection example, the Multicriteria Overlay tool was run for four scenarios varying the methods but using the same criteria and relative importance weights. The methods used were Weighted sum, Weighted geometric mean, Minimum, and Ideal point solution. The Locate Regions tool was then applied to each output.
Regions shared across all four outputs indicate stable, high suitability sites that are not affected by the choice of overlay method, while regions unique to one or two outputs highlight areas where the results depend on how trade-offs are handled. Comparing the four sets of candidate sites revealed how each method's assumptions influenced site selection, helping you choose the most appropriate approach for the study.
Caption: Comparing suitability and Locate Regions outputs across multiple overlay methods using the Multicriteria Overlay tool in ArcGIS Pro
In conclusion, the overlay method that you select can have a significant impact on your results. The various methods allow you to better capture the relative interaction among the criteria, thus resulting in a more accurate model.
The original blog was first published in the ArcGIS Blog, and can be found here: