The key to objectively measuring the benefits of GIS use is to realize that there are two different types of benefits and that different techniques must be used to measure each. Efficiency benefits occur when the same task previously done without the GIS can be done less expensively with the GIS. Effectiveness benefits occur when the GIS allows completion of a task that would not have been done without the GIS. Efficiency benefits can be measured by comparing the variable input costs of performing the application with the GIS to the variable input costs prior to the use of the GIS. Effectiveness benefits depend on the value of the unique GIS output. These benefits can be measured by identifying: (a) how the GIS output is different from the non-GIS output, (b) how this difference affects each user of the GIS output, and (c) the value of each of these effects.