Multi-criteria evaluation and GIS

One of the most important applications of GIS is the display and analysis of data to support the process of environmental decision-making. A decision can be defined as a choice between alternatives, where the alternatives may be different actions, locations, objects, and the like. For example, one might need to choose which is the best location for a hazardous waste facility, or perhaps identify which areas will be best suited for a new development. Broadly, decisions can be classified into two extensive categories – policy decisions and resource allocation decisions. Resource allocation decisions, as the name suggests, are concerned with control over the direct use of resources to achieve a particular goal. Ultimately, policy decisions have a similar aim. However, they do so by establishing legislative instruments that are intended to influence the resource allocation decisions of others. Thus, for example, a government body might reduce taxes on land allocated to a particular crop as an incentive to its introduction. This is clearly a policy decision; but it is the farmer who makes the decision about whether to allocate land to that crop or not. To be rational, decisions will be necessarily based on one or more criteria – measurable attributes of the alternatives being considered, that can be combined and evaluated in the form of a decision rule. In some circumstances, allocation decisions can be made on the basis of a single criterion. However, more frequently, a variety of criteria is required. For example, the choice between a set of waste disposal sites might be based upon criteria such as proximity to access roads, distance from residential and protected lands, current land use, and so on. This chapter focuses on the very specific problems of spatial resource allocation decisions in the context of multiple criteria – a process most commonly known as multi-criteria evaluation