Planimetric Maps Essay Example for Free

Planimetric Maps Essay A planimetric map presents only the horizontal positions for the features represented. It is distinguished from a topographic map by the omission of relief, normally represented by contour lines. Sometimes, it is called a line map. Topographic Map. A topographic map portrays terrain features in a measurable way, as well as the horizontal positions of the features represented. The vertical positions, or relief, are normally represented by contour lines on military topographic maps. On maps showing relief, the elevations and contours are measured from a specific vertical datum plane, usually mean sea level. Photomap. A photomap is a reproduction of an aerial photograph upon which grid lines, marginal data, place names, route numbers, important elevations, boundaries, and approximate scale and direction have been added. Joint Operations Graphics. Joint operations graphics are based on the format of standard 1:250,000 medium-scale military topographic maps, but they contain additional information needed in joint air-ground operations. Along the north and east edges of the graphic, detail is extended beyond the standard map sheet to provide overlap with adjacent sheets. These maps are produced both in ground and air formats. Each version is identified in the lower margin as either joint operations graphic (air) or joint operations graphic (ground). The topographic information is identical on both, but the ground version shows elevations and contour in meters and the air version shows them in feet. Layer (elevation) tinting and relief shading are added as an aid to interpolating relief. Both versions emphasize airlanding facilities (shown in purple), but the air version has additional symbols to identify aids and obstructions to air navigation. Photomosaic. A photomosaic is an assembly of aerial photographs that is commonly called a mosaic in topographic usage. Mosaics are useful when time does not permit the compilation of a more accurate map. The accuracy of a mosaic depends on the method employed in its preparation and may vary from simply a good pictorial effect of the ground to that of a planimetric map. Terrain Model. A terrain model is a scale model of the terrain showing features, and in large-scale models showing industrial and cultural shapes. It provides a means for visualizing the terrain for planning or indoctrination purposes and for briefing on assault landings. Military City Map. A military city map is a topographic map (usually at 1:12,550 scale, sometimes up to 1:5,000), showing the details of a city. It delineates streets and shows street names, important buildings, and other elements of the urban landscape important to navigation and military operations in urban terrain. The scale of a military city map depends on the importance and size of the city, density of detail, and available intelligence information. Special Maps. Special maps are for special purposes such as trafficability, communications, and assault maps. They are usually in the form of an overprint in the scales smaller than 1:100,000 but larger than 1:1,000,000. A special purpose map is one that has been designed or modified to give information not covered on a standard map. The wide range of subjects that could be covered under the heading of special purpose maps prohibits, within the scope of this manual, more than a brief mention of a few important ones. Some of the subjects covered are: * Terrain features. * Drainage characteristics. * Vegetation. * Climate. * Coasts and landing beaches. * Roads and bridges. * Railroads. * Airfields. * Urban areas. * Electric power. * Fuels. * Surface water resources. * Ground water resources. * Natural construction materials. * Cross-country movements. * Suitability for airfield construction. * Airborne operations. If military maps are not available, use substitute maps. The substitute maps can range from foreign military or commercial maps to field sketches. The NGA can provide black and white reproductions of many foreign maps and can produce its own maps based upon intelligence. Foreign Maps. Foreign maps have been compiled by nations other than our own. When they must be used, the marginal information and grids are changed to conform to our standards, if time permits. The scales may differ from our maps, but they do express the ratio of map distance to ground distance and can be used in the same way. The legend must be used since the map symbols almost always differ from ours. Because the accuracy of foreign maps varies considerably, they are usually evaluated in regard to established accuracy standards before they are issued to our troops. Atlases. Atlases are collections of maps of regions, countries, continents, or the world. Such maps are accurate only to a degree and can be used for general information only. Geographic Maps. Geographic maps provide an overall idea of the mapped area in relation to climate, population, relief, vegetation, and hydrography. They also show the general location of major urban areas. Tourist Road Maps. Tourist road maps are maps of a region in which the main means of transportation and areas of interest are shown. Some of these maps show secondary networks of roads, historic sites, museums, and beaches in detail. They may contain road and time distance between points. The scale should be carefully considered when using these maps. City/Utility Maps. City/utility maps are maps of urban areas showing streets, water ducts, electricity and telephone lines, and sewers. Field Sketches. Field sketches are preliminary drawings of an area or piece of terrain. Aerial Photographs. Aerial photographs can be used as map supplements or substitutes to help you analyze the terrain, plan your route, or guide your movement.