Colour Conventions

Traditionally the use of colour in mapping can be divided into qualitative and quantitative agreements. Breaking those, will leave the map reader extremely confused. Now you will probably ask what are qualitative and what are quantitative map agreements?

Qualitative use of colour in mapping addresses points, lines, areas or symbols. The element's colour is seen as a qualitative value, i.e. it is not applying an amount to the elements. Qualitative value is expressed through colour hue and its intensity or saturation. You will recognise in the following examples that the logic of use is appropriate.

Water – Blue
Vegetation – Green
Land – Brown
Climate – Blue to Red

With hues, you can express classes of one and the same amount, but it is hard to associate hue psychologically with varying amounts of data.

Quantitative use of colour may address the same elements as in the qualitative way, but at this time, value differences are best shown with a differing amount of one colour hue for one theme.

Beneath the differentiation between qualitative and quantitative use of colour, in general, there are 4 rules existing, established by E. Imhof, the founder of the Institute of Cartography. They may seem philosophically verbalised, but are essential for designing coloured maps (Imhof 1972, p. 53p).

Rule 1:

Pure, bright or very strong colours have loud, unbearable effects when they stand unrelieved over large areas adjacent to each other. Extraordinary effects can be achieved when they are used sparingly on or between dull background tones.

Rule 2:

The placing of light, bright colours mixed with white next to each other usually produces unpleasant results, especially if the colours are used for larger areas.

Rule 3:

Large area background or base-colours should do their work most quietly, allowing the smaller, bright areas to stand out most vividly, if the former are muted greyish or neutral. For this very good reason, grey is regarded in painting to be one of the prettiest, most important and most versatile colours. Strongly muted colours, mixed with grey, provide the best background for the coloured theme. This philosophy applies equally to map design.

Rule 4:

If a picture is composed of two or more large, enclosed areas in different colours, then the picture falls apart. Unity will be maintained, however, if the colours of one area are repeatedly intermingled in the other, if the colours are interwoven carpet-fashion throughout the other. All colours of the same theme should be scattered like islands in the background colour. The complex nature of the earth’s surface leads to enclosed coloured areas, all over maps. They are the islands in the sea, the lakes on continents, they are lowlands, highlands, etc., which often appear in thematic maps and provide a desirable amount of disaggregation, interpretation and reiteration within the image.