Understanding weights in the suitability overlay

The range of numbers that you select for a scale does not have an inherent value; it is the degree of value in the scale that gives them their value.

For example, if you use a scale of 1 to 10 and assign a weight of 2 to the Road Network layer and a weight of 5 to the Rainfall layer, it has the same effect as using a scale of 1 to 100 and giving Road Network layer a weight of 20 and the Rainfall layer a weight of 50. In each case, the Rainfall layer has more weight and is considered better or more desirable in the calculation.

The scale for the layers is usually based on a scale of 1 to 100, but the sum of the layer weights does not need to equal 100. The point is to identify the relative importance of each layer in comparison with the others.

The scale of the data in the layers does not have to be the same as that used for the layers, but the scale should be consistently applied for all the data. Using different scales for the data in different layers may cause unwanted results.

For example, if you used a scale of 1 to 1000 to rank the data in the Soil Types layer and a scale of 1 to 10 for the data in the other layers, the soil types might nullify the importance of other data like rainfall even if the Rainfall layer itself has a higher weight than the Soil Type layer.