Cartographic Generalization

the processes of selection and summarizing of the contents in drafting geographical maps. The purpose of such generalization is to preserve and distinguish on a map the main and typical outlines and the characteristic peculiarities of the features shown in accordance with the function, subject, and possible scales of the map. Map scale has the most obvious effect on cartographic generalization. For example, the representation of an area of 1 sq km on a map with a scale of 1:1000 will occupy an area of 1 sq m; with a scale of 1:10,000, 1 sq decimeter; with a scale of 1:100,000, 1 sq cm; and with a scale of 1:1,000,000, 1 sq mm. The depiction of a locality in all of these scales with identical detail and saturation is impossible. The exclusion of details and less important elements is inevitable as the scale becomes smaller. However, the effect of the scale is not only to limit the amount of space available on the map: on a small-scale map, which covers considerable area, details lose their significance and, if retained, would make it more difficult to perceive the main objects on the map. For example, an overall picture of the mountain systems of the Caucasus can be conveyed only on a small-scale and very generalized map, not on detailed topographical maps. Cartographic generalization is influenced by geographical conditions: the same features (or their peculiarities) are evaluated differently for different landscapes or according to the special nature of their relationship to other features—for example, wells are an important element in all topographical maps of desert and semidesert regions, but they are not indicated on similar maps showing areas with good water supply. Cartographic generalization is particularly affected by the function of the map. For example, in the case of a reference map, as much information as possible is provided, whereas on an educational map of the same scale the number of features shown will be reduced and limited to the requirements of the school program.

Cartographic generalization may appear in the following ways: (1) the selection of objects (the restriction of the contents of the map to objects that are essential), (2) the carefully considered simplification of contours (the planned outlining of objects, both linear and those that occupy an area, in which the peculiarities of the outlines typical of such objects are maintained and sometimes even emphasized—the sickle shape of oxbow lakes or the circular shape of lakes on out-wash plains), (3) the generalization of quantitative characteristics by reducing the number of divisions within which quantitative differences for specific features shown on the map are indicated (for example, in the case of a population scale for built-up areas, combining two divisions on the scale, such as “less than 500 inhabitants” and “from 500 to 2,000 inhabitants” into one division, “less than 2,000 inhabitants”), (4) the generalization of qualitative characteristics by simplifying the classifications for the features being shown (not subdividing forests according to type when showing vegetation on topographical maps (not subdividing forests according to type when showing vegetation on topographical maps), and (5) the replacement of individual features by general designations (indicating a population center by blocks and a geometrical sign instead of marking individual buildings).

The establishment of the principles governing cartographic generalization is an important scientific problem of cartography. An example is the establishment of rules of selection in a mathematical form, particularly in the form of quantitative indexes, the criteria that determine the conditions for indicating on the map objects of various categories (for example, the obligation to indicate all cities having 10,000 or more inhabitants). The selection indexes vary according to the map and the geographical region. The development of the mathematical bases of cartographic generalization has acquired considerable importance as a result of the introduction of automation into the processes of drafting and use of maps.