Topographic Cartography

(the Russian term, topografila, conforms to European usage), the scientific and technical discipline dealing with the geographic and geometric study of a locality through the compilation of topographic maps based on ground, aerial, and space surveys.

Topographic cartography is regarded by some authorities as an independent branch of cartography dealing with the problems of detailed general geographic mapping of a territory; others treat it as a branch of geodesy, devoted to problems of measurements on the earth’s surface and based on the use of aerial photographs for the determination of the position, shape, and dimensions of the natural and man-made objects being recorded. The discipline includes questions of the classification, content, and precision of topographic maps and methods of mapping, updating of maps, and map-reading. Each country regulates these matters by imposing its own standards. Although the standards are related to economic and political factors, the organizational and technical capabilities of cartographic and geodetic services, and the nature of the landscape, they are quite similar on the whole; as a result, it is possible to compile comparable topographic maps. Among the most important tasks of topographic cartography are the periodic modernization of the standards and refinement of map symbols and the basic principles for the selection and generalization of the content of maps according to scale and the characteristics of the territory (seeCARTOGRAPHIC GENERALIZATION).

The first surveying for the purpose of making topographic maps was done in the 16th century. Ground surveying, which graphically transmits the location and characteristics of terrain objects and which is based on precise instrumental measurements, developed in the 18th century. Aerial photographic surveying was introduced in the first third of the 20th century, and space photography developed in the 1960’s. At present, ground methods are used in topographic cartography primarily for regions in which other mapping methods are unprofitable because of their small area or where the nature of the territory presents difficulties. Plane-tabling, which is performed entirely in the field, is used in the first case; phototheodolite surveying, or ground photogrammetric surveying, where part of the work is done in the field using a phototheodolite and the rest is done indoors with photogrammetric instruments, is used in the second case, in many mountainous regions. The use of data from space photography has thus far been limited to the compilation of survey maps and small-scale topographic maps, mainly in undeveloped and little-studied territories in the polar regions, deserts, and jungles, and for the identification and selection from space photographs of the areas on the earth that should be studied first by conventional aerial photographic surveying in order to make or update medium-scale and large-scale topographic maps.

Combined and stereotopographic aerial photographic methods are the main methods currently used (seeAERIAL PHOTOGRAPHY). In a combined survey, all operations, rather than just the aerial photographic survey, are performed in the field. The other facets of the survey include construction of the map base, the drawing of relief, and the interpretation of objects and contours on the plan photograph. In stereotopographic surveying, which is more effective, aerial photography and radiogeodetic work to create the survey framework of the map are done in the air, whereas construction of a reference geodetic grid, identification of standard sectors, and entry of objects not shown in the aerial photographs are done on the ground. The remaining mapping processes are done indoors; these include construction of photogrammetric grids to develop the framework, stereoscopic drawing of the relief, and interpretation of the aerial photograph of the entire survey area. The reduction of fieldwork, particularly by improving regional technological schemes of topographic surveying, is a very important task of topography.

The updating of topographic maps, in which the content of the maps is brought into line with current requirements and the condition of the locale, is an independent, increasingly sophisticated technique of topographic cartography. The updating may be periodic (from 3–4 to 12–15 years) or continuous, depending on the characteristics of the region; in both cases it should be based on aerial photographic surveying and data of cartographic significance, such as plans for land and forest use, records of construction in cities, navigation charts, linear plans of roads, charts of power transmission lines, and handbooks of administrative and territorial divisions. This makes it possible to do most of the work indoors. In the updating of maps, supplements and corrections are necessary primarily for man-made objects, such as population centers, roads, and croplands. Updated maps should be as precise as new maps produced by surveying in the particular scale. Photoelectronic aerial surveying, particularly radar surveying, is used in updating maps and, to a lesser degree, for drawing maps by surveying methods. (Aerial black-and-white or color photography, however, is the primary means of obtaining information about a locale.)

The latest development in topographic cartography is the introduction of automation in the compilation of topographic maps. Practically useful results have already been produced by the use of computers to perform several functions. Computers can read information from aerial photographs and record the information in digital form, and can also perform automatic conversion of the digital information—including transformation from a central to an orthogonal projection, drawing the relief in contour lines and interpreting some objects—during the compilation of original maps using various devices and during the process of engraving or drawing originals for publication.

Automatic equipment can be used in topography not only for the compilation of maps but also for the construction of digital models of the terrain, which are formalized models represented by the coordinates and characteristics of terrain points recorded in digital code—for example, on magnetic tape—for subsequent computer processing. These models have two main uses. First, they can be used to add to a map data that are not expressed in either graphic or photographic reproduction of the terrain but that are very important for many studies, above all land use and city planning. Second, they can single out information contained on maps—for example, objects of a particular type, types of territory, and sets of data—that is important for the solution of such technological problems as selecting the routes of canals, roads, and pipelines, and deciding on the sites of reservoirs, airports, and forest plantings. The digital form also makes it possible to encode and retrieve essential cartographic materials when they are concentrated in reference information files. Automatic remote methods of obtaining topographic data have made possible preliminary surveying of the surface of the moon and some of the planets. This in turn has led to the production of various types of maps. Among the products of remote surveying have been series of survey maps for large areas, individual topographic map sheets for selected sectors, and large-scale maps of the locales around the landing points of interplanetary automatic stations and spacecraft and along the routes of lunar vehicles.