Cartographic Methods of Presentation

Cartographic Methods of Presentation


graphic methods used on maps to show the spatial arrangement of phenomena and their combinations, relationships, and development. A special system of characters—the cartographic symbols, which are summarized and systematized in a relatively small number of cartographic methods of presentation—is used in cartography for this purpose. The primary methods include those of signs, line symbols, isolines, and the qualitative background; angle diagrams; the point method; area patterns; signs of motion; and collation and choropleth maps.

The sign method (nonscale signs) is used for objects that are not expressed in the scale of the map and are usually used to represent phenomena that are localized at points. The signs indicate the location and type of the objects and may also describe their size, importance, or change over time (for example, symbols for populated points that indicate the type of settlement, population, and administrative significance). The shape, size, and color of the signs are used to represent the characteristics of the objects being mapped. The symbol may have a geometric shape, it may be a letter of the alphabet, or it may resemble in outline the object being represented. Geometrically shaped signs whose area is proportional to the numerical index of the objects being shown are often used—for example, proportional to the number of workers when mapping industrial enterprises or centers.

Line symbols are used to show political and administrative borders and power lines and for linear objects whose width is not expressed in the scale of the map (for example, roads and rivers). The qualitative and quantitative characteristics of linear objects are shown by the type of lines (for example, various dotted lines) and the color and the width of the symbols.

The isoline method is used to convey the quantitative characteristics of phenomena that are continuous and change gradually in space (for example, terrain and climatic phenomena).

The qualitative background method shows the breakdown of a territory (its regionalization) according to some particular natural, economic, or political and administrative features. It is used for qualitative description of phenomena that are continuous over the earth’s surface (for example, soil cover) or have a large-scale scattered distribution (for example, population). The first step is the development of a classification of the phenomenon being mapped; the territory then is divided according to the classification into qualitatively homogeneous parts (districts, regions, and so on). Finally, areas belonging to the same class are given the color assigned to the particular type or hachured accordingly.

Angle diagrams (that is, diagrams related to definite points) are used to describe seasonal and other periodic phenomena (the annual course of temperatures and precipitation; changes in snow cover), the frequency and velocity of winds from various directions (in the form of wind roses), and the frequency and velocity of ocean currents.

The point method is used to map large-scale scattered phenomena (rural population, croplands, and livestock farming). For this purpose a definite number of objects (units) is symbolized by a point (more precisely, a small circle) located at the place on the map where the objects actually exist. As a result a certain number of points of equal magnitude and identical significance are written on the map; their grouping (density) gives a graphic picture of the location of the phenomenon, and their number makes possible determination of its dimensions or the number of objects.

Area patterns, or areas of distribution of some particular phenomena (various species of plants and animals; various types of farmland) are shown on maps by contouring a section with a solid or dotted line of definite design or by coloring or hachure. The diversity of methods for representing ranges makes possible the combination of a number of ranges on the same map, even if they overlap.

Signs of motion are used for natural and social phenomena (ocean currents, migration of birds or population, shipping, and directions of military strikes).

Graphic methods are widespread, above all vectors (arrows), which may be used to characterize the speed, stability, power, and other features of the phenomena by differences in their shape, size, and color. A second common method is bands (strips) for passenger and cargo flows, which are laid out along the routes of movement; their width usually indicates the size of the flow.

Collation and choropleth maps are used for a graphic spatial representation of statistical data (for example, population data) that are being processed or published in summary form, as applied to administrative or other territorial divisions rather than individual points or objects. Collation maps show the distribution of a phenomenon by means of diagrams that are located within units of the territorial grid and express the total magnitude of the phenomenon (for example, the amount of arable land) within the borders of each territorial unit. The choropleth map is a method of showing the average intensity of a particular phenomenon (average population density, percentage of land under cultivation, and so on) within definite territorial units, most often administrative units. In this case each territorial unit is colored or hachured so that the intensity of the color or hachure indicates the intensity of the phenomenon.