It is fairly likely that the first analysis method you encountered in learning about GIS was overlay, where information from several different GIS layers is combined to enable complex queries to be performed. In this lesson, we will examine both the fundamentals of overlay, particularly the importance of registering layers to the same geographical coordinate system, and more elaborate versions of the method. As will become clear, overlay analysis can be generalized to almost any operation involving multiple map layers and is therefore very close to map algebra as discussed in the previous lesson.
The Multi-criteria decision analysis (MCDA) method (also known as surface overlay methods) are a set of methods that are used to combine different criteria. Criteria are ranked indicating their strength and importance of membership in a set. A number of different types of membership or overlay method can be used. These include: