Psychologists use experiments on humans and other animals to observe how physiological and intellectual processes work. Recently scientists from many different disciplines have been developing tools that permit us to see the area or geographic distribution of many things, from land use to human behaviour. This new set of tools of observation is generally called Geographic Information Systems, or GIS. One especially useful potential emerging from GIS is the capacity to use remotely sensed data in computerized analyses. Remote sensing can be done from aeroplane fly-overs, but massive coverage is available from satellite imagery, which is becoming both more refined and cheaper. The advantages of the new electronic imagery are immense. The fact that images are electronic, rather than chemical means that they can be computer enhanced. The electronic imagery also makes it possible to distinguish built up areas from vegetation, and thus to measure precisely the number of hectares of an urban area.