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The fundamental of cartographic generalisation, the reduction of the amount of information which can be shown on a map in relation to reduction in scale, is examined. The Principle of Selection was first proposed by Töpfer in 1961, and is expressed as an equation relating the number of occurrences of a particular feature at source map scale and at derived map scale. The application of this to small-scale maps involves the introduction of two constants to represent symbolic exaggeration and symbolic form. Examples are given and illustrated. The paper is accompanied by explanatory notes by Dr D. H. Maling, who presented the paper on behalf of the authors at the XX International Geographical Congress London 1964, Section IX, Cartography.
Töpfer et al. (1966) studied this question.