The ward cartogram drawn using Theisson polygons.

Theisson polygons constructed around the centroids of 10,444 census wards from the 1981 census equal population cartogram software by author on an Archimedes computer and E.S.R.I. on a Sun computer.

One way of subdividing space when, for instance, only centroids are known, is to drawn Theisson polygons around the points. Traditional geographic information systems often cannot cope with overlapping or empty spaces, but must have a mutually exclusive set of polygons on which to operate. The resulting image is quite elegant, and the problem of the coastal boundary is well illustrated.