Topographic maps are miniature models of earth's three-dimensional surface, printed on two-dimensional pieces of paper. Lines of equal elevation (i.e., the coastline and 300-ft line). the magnetic pole migrates very slowly, so the declination is exact only for the year listed on the map. also shown is the declination between compass north (star symbol) and grid north (GN). Magnetic compasses are attracted to the magnetic north (MN), currently located northwest of Hudson Bay in Northern Canada, about 700 km (450 mi) from the true north pole.Ī compass-like symbol on the bottom margin of topographic maps, which shows the difference in degrees between compass north (MN) and true north (usually a star symbol). this is called grid north (GN) and is usually the same direction as true north on the actual earth. Each 15-minute map can be divided into four 7.5-minute maps.īecause longitude lines form the left and right boundaries of a topographic map, north is always at the top of the quadrangle. A 15-minute topographic map represents an area that measures 15 minutes of latitude by 15 minutes of longitude. the numbers refer to the amount of area that the maps depict, in degrees of latitude and longitude. Quadrangle maps are published in several sizes, but two are most common: 15-minute quadrangle maps and 7.5-minute quadrangle maps. Longitude is measured in degrees east or west of the prime meridian, a line that runs from the north pole to the south pole through greenwich, england.įor finer measurements each degree can be subdivided into 60 equal subdivisions called minutes ('), and the minutes can be divided into 60 equal subdivisions called seconds ("). latitude is measured from zero degrees at the equator to ninety degrees North (at the north pole) or 90 degrees south (south pole). Latitude and longitude are both measured in degrees. The contour lines are the most distinguishing features of a topographic map.Ī section of Earth's surface that is bounded by lines of latitude at the top (north) and bottom (south) and by lines of longitude on the left (west) and right (east). It shows landforms (hills, valleys, slopes, coastlines, gullies) and their relief (difference in elevation) by using contour lines to represent elevations of hills and valleys. A two-dimensional (flat) representation (model) of a three-dimensional land surface (landscape).
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