What is a weighted overlay?

In many suitability analyses, some eligibility criteria are more important than others. Often, it is the expectation in a location search to be able to compare several suitable candidates whether, and how strongly, they meet a set of criteria of differing importance. By using the layer principle, one can easily extend the overlay by assigning levels of importance to each criterion.
A numerical weighting factor is assigned to each thematic layer according to its relative importance compared to all other layers. After that, the weighted layers are overlaid as before. This process is called weighted overlay. In principle, weighted overlay is possible with rasters and vectors just like Boolean overlay. For example, wolf experts in St. Gittal could explain that the forest, due to its protective nature, is 1.5 times more important for the wolf than steep and rocky terrain. The corresponding weights would be: weight factor 3 for the forest layer but only 2 for the terrain layer. It should be noted that value ranges of the input data layers should correspond to a range between suitable and not suitable (e.g. from 0 to 1). In the resulting suitability layer, the areas or locations with high values are the most suitable.