Choropleth Maps Without Class Intervals?

It is now technologically feasible to produce virtually continuous shades of grey by using automatic map drawing equipment. It is therefore no longer necessary for the cartographer to "quantize" data by combining values into class intervals. As a simple illustration an automatic line plotter can be programmed to draw lines virtually any distance apart (Fig. 1). Thus, one can obtain any desired density of inked area to white area. For example, if the geographical data, symbolized by z, are normalized to lie in the range from zero to one, then an appropriate spacing of orthogonal lines of width w is given by s = (w/z) • [1 + (1 — z)].