A way of combining a collection of very large datasets into classes, both to make subsequent analysis simpler and to provide a more generalized account of a phenomenon. For any analyses based on areal units, the problem is one of scale: that plotting geographical information on the wrong scale can conceal information that only becomes apparent at other scales and resolutions. Openshaw (1977) TIBG 2, 4, 459 offers a closely argued mathematical inquiry into this problem and suggests a solution to it; his conclusion is important to statisticians and non-statisticians alike: ‘geographers and other spatial disciplines should pay far more attention to the way in which they design their zoning systems for spatial study’.