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Еlevation and Relief
The elevation of points on the ground and the relief of an area affect the movement and positioning of military units. Relief is the representation of the shapes of hills, valleys, streams, or terrain features on the earth's surface. Mapmakers use several methods to depict relief of the terrain. Layer tinting is a method of showing relief by color. Hachures are short, broken lines used to show relief. Relief shading indicates relief by a shadow effect achieved by tone and color. A contour line is an imaginary line on the ground, above or below mean s ea level which represents vertical positionsor relief. The elevations and contours are measured from a specific vertical datum plane. Scale The scale is expressed as afraction and gives the ratio of map distance to ground distance. The numerical scale of a map indicates the relationship of distance measured on a map and the corresponding distance on the ground. This scale is usually written as a fraction and is called the representative fraction. According to the Defense Mapping Agency maps are classified by scale into three categories. They're small, medium , and large-scale maps. The terms small scale, medium scale and large scale may be confusing when read in conjunction with the numbers. However, if the number is viewed as a fraction, it quickly becomes apparent that 1:600,000 of something is smaller than 1:75,000 of the same thing. These maps with scales of 1:75,000 and larger are used for tactical, administrative, and logistical planning. The standard small scale map is 1:1,000,000. This scale map covers a very large ground area, so mapmaker has hardly any room for details. Medium maps are used for planning operations, including the movement and concentration of troops and combat vehicles. The standard large scale map is 1:50,000. A graphic scale is a ruler printed on the map and is used to convert distances on the map to actual ground distances. On a 1:250,000 scale map, the prescribed symbol for a building covers an area about 500 feet square on the ground; a road symbol is equivalent to a road about 520 feet wide on the ground; the symbol for a single-track railroad is equivalent to a railroad cross-tie about 1,000 feet on the ground. Types The map of choice for land navigation is the 1:50,000-scale military topographic map. All maps are subdivided by types. Planimetric map is a map that presents only the horizontal positionsfor the features represented. Sometimes, it is called a line map. It is distinguished from a topographic map by the omission of relief, normally represented by contour lines. Photomap is a reproduction of an aerial photograph upon which grid lines, marginal data, route numbers, and approximate scale and direction have been added. Photomosaic is an assembly of aerial photographs, when time does not permit the compilation of a more accurate map. Terrain model provides a means for visualizing the terrain for planning and for briefing on assault landing. Military city map is a topographic map showing urban elements of military importance that are compatible with the scale of map. A special purpose map has been designed to give information not covered on a standard map. Some of the subjects covered are: terrain features, drainage characteristics, vegetation, coasts and landing beaches, urban areas, cross-country movements. Дата добавления: 2015-09-18 | Просмотры: 578 | Нарушение авторских прав |