Mapping Continuous Geographical Distributions Using Dot-Density Shading
Stephen J. Lavin · The American Cartographer · 1986
Dot-density shading is proposed as an automated method of representing continuous geographical distributions. Clusters of dots, each representing a value in a gridded data matrix, are scaled proportionally to data intensity. Dots are plotted by quasi-random dot placement that assures non-overlap of dots, accurate proportions of dot coverage, and is algorithmically efficient. Dot-density shading was developed as an adjunct to isoline mapping, and appears to present better thematic views of spatial trends in continuous data. On the other hand, isoline maps are more effective vehicles for data storage and extraction. Both types of maps can be used together because of their complementary informational character. Examples of isoline and dot-density maps for identical data are shown; scaling and plotting algorithms are explained; and interpretational examples are given.