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A topographic map is a map that shows the actual shape of the landscape and the various heights of the landscape. The map allows geographers to see the height and shape of the land by using contour lines. Contour lines are lines that join together all points that have the same height above sea level. The height between contour lines is called the contour interval. The map on the opposite page has various contour lines with an interval of 50 metres. The numbers on the contours show how high the land is above sea level. Mount Florence, for example, is more than 400 metres above sea level. The map also shows that some contour lines are close together while other contour lines are far apart.
Close contours mean that the slope of the land is steep; contours well apart mean that the slope of the land is gentle. The closer the contours, the steeper the slope. The further apart the contours, the latter the slope. Therefore, on the map on this page, the land around X is steeper than the land around Y. The relative steepness of the slope is called the gradient. Topographic maps also show in detail both the natural and human features of the landscape. Natural features include rivers, lakes, swamps, hills and beaches. Human features include roads, towns, railways and dams. Topographic maps use conventional signs and symbols to show water, rivers, vegetation, roads, railways and buildings. The meaning of each sign or symbol is explained in a key, or legend.
ColoursDifferent colours are also used on topographicmaps to indicate certain features, for example:· brown is used for natural features, includingcontour lines· blue is used for all water and river features· green is used for vegetation and ground cover· black and red are used for human featuressuch as roads, railways and buildings.
Topographic maps also use lines to help us locate places on a map. These lines are overprinted to form a grid. These grid lines are given as twodigit numbers that appear on the margins of the map. The lines that run up and down the map (north±south) are called eastings because the numbers increase the further east they are. The lines that run across the map horizontally (east± west) are called northings because the numbers increase the further north they are. When stating location, the eastings are given first, then the northings.
Area references and contour lines on a topographic mapAn area reference is a four-figure reference that tells us the grid square in which to and a feature. On the map opposite, the railway station is located at 8640. The letters AR are usually placed in front of an area reference, so the area reference for the railway station is AR8640. A grid reference is a six-figure number that shows an exact point in the grid square. The third and sixth figures represent one-tenth of the distance between the two grid numbers. However, these divisions are not written on the map, so they must be estimated. The letters GR are used in front of a grid reference. The grid reference for point Y on the map above is GR643146. There are no spaces between the digits in references.