topographic map(redirected from Topo map)
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topographic map[¦täp·ə¦graf·ik ′map]
a detailed geographic map of uniform content, design, and mathematical basis. Topographic maps depict the natural and socioeconomic objects of a region with their qualitative and quantitative characteristics and specific features of their location. Topographic maps are intended for various economic, scientific, and military applications. They are constructed according to the laws of the projection of three-dimensional bodies onto a plane and have a reference grid and consistent system of symbols. This makes it possible to obtain graphic and precise general geographic information about an area, which can be compared for different scales, regions, and years of surveying. Because of their documentary nature, topographic maps can be used as sources of detailed information about a particular territory and as a reliable means of orientation on the terrain. They are also useful for the study of a locale and of many manifestations of natural processes and human activities, as well as for the establishment of the content, boundaries, and areas of sections of land, the position and elevation of points and the distances and inclines between them, and for other measurements and calculations. Topographic maps are essential for conducting various types of investigations and engineering surveys and as the basis for recording their results, for compiling plans for the transformation of areas, for drawing thematic maps dealing with various branches of the economy (see), and for rational economic management and nature conservation.
A distinction is made between small-scale (survey), medium-scale, and large-scale topographic maps. The scales, projections, content, and precision of maps in each of these groups are relatively close in various countries, including maps in the USA and Great Britain, some of which are not in the metric system. In the USSR the first group includes maps with scales of 1:1,000,000 and 1:500,000; the second group has scales of 1:200,000 and 1:100,000, 1:50,000, 1:25,000 1:10,000, and 1:5,000; and the third group includes scales of 1:2,000, 1:1,000, and 1:500. Small-scale topographic maps are made from large-scale topographic maps, mainly by means of map compilation procedures; data from high-altitude aerial surveying and space photography have come to be used for the same purpose. Medium-scale topographic maps are made or updated primarily by means of aerial photography. Large-scale topographic maps are produced by the same methods, and also by ground surveying, particularly planetabling.
Topographic maps are drawn in cartographic projections that make possible the attainment of complete geometric similarity to the contours of the locale and the maintenance of a constant scale in all directions. This is because distortions owing to the projection in this case are less than the possible precision of measurement using the maps. In the Soviet Union and the other member countries of the Council for Mutual Economic Assistance (COMECON), the Gauss-Krüger conformal transverse cylindrical projection computed according to elements of the Krasovskii ellipsoid has been adopted for topographic maps (an exception is the 1:1,000,000 map, which throughout the world is constructed in a modified polyconic projection used as a polyhedral projection). For small-scale and medium-scale topographic maps, the earth’s surface is projected in zones 6° wide. Large-scale maps are based on 3° zones, and an independent system of grid coordinates is constructed for each zone, using the equator and the central meridian of the zone as axes. Therefore, unlike other geographic maps, topographic maps have both a degree grid of longitude and latitude and a kilometer grid. The geodetic references for Soviet topographic maps in plan are the triangulation and traversing points in the 1942 unified system of coordinates; the leveling points in the Baltic system of elevations (from 0 on the Kronstadt tide gage) are used for elevation. In the compilation of topographic maps, these reference points are developed by instrumental methods adopted in geodesy and photo-grammetry, and the so-called plan-elevation map base is produced. The criteria of map precision are the mean and maximum errors in the position of points on this base relative to points of the geodetic reference system and in the position of contours and terrain features, elevation markers, and horizontals relative to the closest points of the map base itself. Permissible errors differ depending on the scale and the territory being mapped (for example, open and forested land).
Each sheet of a topographic map is a trapezoid bounded by straightened arcs of meridians and parallels; the size of the trapezoid is determined by the scale of the map and the latitude of the locale. Topographic maps are usually published in multisheet series with a particular system of drawing lines and numbering the sheets. These systems are based on a map sheet with a scale of 1:1,000,000 using international ruling (dimensions of 4° of latitude and 6° of longitude), marked with Latin letters and arabic numerals. For sheets of maps of larger scale covering the same territory, other letters and numbers are added to the original system according to the breakdown of the smaller-scale sheet into a definite number of parts. According to the scheme used in the USSR, topographic maps are given the following designations: N-37 for a sheet of a map on a scale of 1:1,000,000; N-37-G for 1:500,000; N-37-XXXVI for 1:200,000; N-37–144 for 1:100,000; N-37–144-G for 1:50,000; N-37–144G-g for 1:25,000; N-37–144G-g-4 for 1:10,000; and N-37–144(256) for 1:5,000. For small-scale and medium-scale topographic maps, the identification number always makes it possible to determine not only the scale but also the geographic position and area of the territory depicted on a particular sheet. The areas of the sheets listed above are 175,000, 43,780, 4,860,1,220, 305, 76,19, and 4.8 sq km, respectively. By convention, large-scale topographic maps of sectors, unlike other topographic maps, are ruled into standard squares of 50 × 50 cm instead of a trapezoid. A map sheet on a scale of 1:5,000, divided into four parts, is used as the starting point for designating such maps; each part is then subdivided, and so on. As a result, large-scale topographic maps receive designations such as 1-G for a scale of 1:2,000, 1-G-IV for 1:1,000, and 1-G-16 for 1:500.
The content of topographic maps—that is, the information about the locale expressed in map symbols—is generally highly standardized. There are, however, a number of particular features, which are determined by the scale and specific purpose of the map and the type of locale.
Topographic maps show the following items: (1) hydrographic network and related natural formations such as bars and Aufeis, (2) discharges of groundwater, (3) the surface relief, shown by contour lines, elevation markers, and additional designations for cliffs, brows of hills, and washouts, (4) the tree, shrub, and grass vegetation, with a breakdown by distinct types of cover, (5) rocky, sandy, and other areas, (6) glaciers and névé fields, (7) swamps and solonchaks, with an indication of their passability, (8) primary agricultural lands, such as arable lands, plantations, and orchards, (9) populated areas, with an indication of their structure, type (city, workers’ settlement, and so on), administrative importance, and size, (10) various buildings and structures, (11) geodetic points and local landmarks, (12) railroads and vehicle and cart roads, power transmission lines, pipelines, and enclosures, and (13) borders of various ranks.
Topographic maps also give numerical descriptions of objects, explanatory captions, and geographic names. The level of detail in representation of the locale is regulated by special standards; and those adopted for representation of relief are particularly important (see Table 1). A system of selection and generalization of contours has also been developed. According to this system, the most significant elements are singled out, with corresponding exclusion of details; outlines are simplified, and groups of symbols and characteristics are replaced by one common symbol or characteristic. For example, on a map with a scale of 1:5,000 every building in cities is identified, whereas for a map with a scale of 1:25,000 the built-up part of a block is shown, a 1:100,000-scale map shows the block as a whole, and a 1:500,000-scale map gives the general contour and basic layout of the city. (See alsoCARTOGRAPHIC GENERALIZATION.) The USSR has a uniform system of editing to ensure that topographic maps have the required content. This system is followed in all primary stages of the compilation or updating of maps, from the design of the aerial survey plan for a particular sector to an editorial check of the proofs.
The margins of the sheet contain the identification number of the topographic map, the name of the appropriate administrative unit and principal populated area, the numeric and linear scales, and information on the systems of coordinates and elevations, the cross section of the relief, and the method and year of manufacture of the map. In addition, the margins of small-scale topographic maps give symbols for the particular sheet, the scale for steps of elevation, and a diagram of borders; medium-scale maps
|Table 1. Height of cross section of relief using contour lines on Soviet topographic maps|
|Scale||Type of relief|
|Flat plains with slopes up to 2°||Plans and hilly areas with slopes up to 6°||Foothill and mountain areas||High mountains|
|1:1,000,000. . . . . . . . . . . . . . . . . . . . . . . .||50||50||100||200|
|1:500,000. . . . . . . . . . . . . . . . . . . . . . . .||50||50||100||100|
|1:200,000. . . . . . . . . . . . . . . . . . . . . . . .||20||20||40||40|
|1:100,000. . . . . . . . . . . . . . . . . . . . . . . .||20||20||20||40|
|1:50,000. . . . . . . . . . . . . . . . . . . . . . . .||10||10||10||20|
|1:25,000. . . . . . . . . . . . . . . . . . . . . . . .||2.5||5||5||10|
|1:10,000. . . . . . . . . . . . . . . . . . . . . . . .||1 or 2||2(2.5)||5||—|
|1:5,000. . . . . . . . . . . . . . . . . . . . . . . .||0.5 or 1||1 or 2||2 or 5||—|
|1:2,000. . . . . . . . . . . . . . . . . . . . . . . .||0.5 or 1||0.5, 1 or 2||2||—|
|1:1,000. . . . . . . . . . . . . . . . . . . . . . . .||0.5||0.5 or 1||1||—|
|1:500. . . . . . . . . . . . . . . . . . . . . . . .||0.25 or 0.5||0.5 or 1||1||—|
also have a diagram of the convergence of meridians and magnetic declination, the range of horizontal equivalents, and additional designations for objects. The margins of small-scale topographic maps contain the name of the area, a diagram of the entire survey sector, and notes on the purpose of the plan, correlation of water lines, and the like. Multicolor printing processes are used for medium-scale topographic maps. Large-scale maps may be printed in many colors or a single color, and topographic plans are duplicated in several copies by photographic, electro-graphic, or other simplified methods.
In the Soviet Union, small-scale topographic maps are used for general geographic study of large regions of the country, as well as for general planning for nationwide and republic-wide measures for the development of natural resources and for economic expansion; they can also be used as flight charts. Ordinary topographic maps are essential for all stages of planning and surveying in such areas as land reclamation, agriculture and forestry (inventory and organization of land and forest use), geological prospecting, exploitation of useful minerals (mining and petroleum and natural-gas industries), planning and construction of population centers, and industrial, hydroelectric, agricultural, transportation, and other types of construction. Large-scale topographic maps are used in the production of working drawings, for the subdivision of plots of land, and in mining and construction jobs. All the COMECON countries are producing specialized topographic maps designed primarily for use in a particular sector in addition to the general, multipurpose maps.
In some cases the type and scope of the required data for large-scale maps and plans are incompatible with the standard content of conventional maps. This leads to the production of parallel maps—for example, topographic maps for agriculture and for the extractive industry. In other cases a specialized map can be produced by adding material to a conventional map; an example would be a topographic map for land reclamation. Another new type of topographic map that is being adopted in practice is the photomap, which combines an aerial photograph with a depiction of the locale using lines and standard symbols. Marine topographic maps of the shelf zone are being developed.
REFERENCESSee references under TOPOGRAPHY.
L. M. GOL’DMAN