Module 6 - Applications in GIS - Suitability Analysis

This week in Applications in GIS we practiced suitability analysis, in which several criteria are overlaid and the overall most suitable areas for a particular need or phenomenon are generated.  We studied two types of analysis.  The first is Boolean, sometimes referred to as binary suitability analysis.  Areas are deemed either suitable, or not suitable, based on the criteria of interest.  For example, any area with a slope greater than 3 degrees might be classed as unsuitable, while any area with a slope of less than 3 degrees might be suitable.  Several criteria can be combined, such as distance to roads or streams, types of land cover, price of land, etc..  Areas in which all criteria are suitable are then considered generally suitable for the purpose at hand.

The other type of suitability analysis is more flexible, because the criteria are judged on a scale of suitability values, and may be assigned different weights or degrees of relative importance.

The figure above shows two scenarios for land suitability depending on slope, land cover, soil, distance from streams and distance from roads.  In the map on the left, all 5 criteria are rated on a scale of 1-5 and weighted with equal importance.  In the map on the right, slope is twice as important, and distances to streams and roads are half as important. This area contains a flat-floored valley in the center, with mountains on either side.  Therefore, making slope more important (with low slope being most suitable) produces larger areas of both "Very High" suitability areas (dark green) and "Low" suitability areas (dark red), as in the case of the right-hand scenario.    In the analysis with equally-weighted criteria (left), there are larger areas of neutral or somewhat high suitability, but smaller areas of very low or very high suitability.  Although 5 suitability classes (Very Low to Very High) were applied to the individual criteria in this exercise, the combinations of all of the criteria did not produce any areas that can be considered of generally "Very Low" suitability.