MSL101L04 Basic Map Reading SR.pdf lesson 4.pdf

Definitions 9 1 the reference or start point for

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DEFINITIONS 9-1. The reference or start point for vertical measurement of elevation on a standard military map is the datum plane or mean sea level, the point halfway between high tide and low tide. Elevation of a point on the earth’s surface is the vertical distance it is above or below mean sea level. Relief is the representation (as depicted by the mapmaker) of the shapes of hills, valleys, streams, or terrain features on the earth’s surface. 9-2. Digital terrain is only accurate to the level of data input and display capabilities of the device, software, and the user display being accessed by the Soldier. These digital devices, systems, simulators, and simulations use digital terrain models and digital elevation models to express map data. Generally digital terrain models represent the sloped contour surface of the earth, without representation of man-made objects and vegetation. The digital elevation model represents the sloped contour surface of the earth, along with surface features such as man-made objects and vegetation. The depiction or exclusion of the map data including elevation, relief, terrain shapes, and terrain features is based on the system and software accessed. METHODS OF DEPICTING RELIEF 9-3. Mapmakers use several methods to depict relief of the terrain: layer tinting, form lines, shaded relief, hachures, and contour lines. 9-4. Layer tinting is a method of showing relief by color. A different color is used for each band of elevation. Each shade of color, or band, represents a definite elevation range. A legend is printed on the map margin to indicate the elevation range represented by each color. However, this method does not allow the map user to determine the exact elevation of a specific point—only the range. 9-5. Form lines are not measured from a datum plane. Form lines have no standard elevation and give only a general idea of relief. Form lines are represented on a map as dashed lines and are never labeled with representative elevations. 9-6. Relief shading indicates relief by a shadow effect achieved with tone and color that result in the darkening of one side of terrain features such as hills and ridges. The darker the shading, the steeper the slope. Shaded relief is sometimes used in conjunction with contour lines to emphasize these features. 9-7. Hachures are short, broken lines used to show relief and are sometimes used with contour lines. They do not represent exact elevations, but are mainly used to show large, rocky outcrop areas. Hachures are used extensively on small-scale maps to show mountain ranges, plateaus, and mountain peaks. 9-8. Contour lines are the most common method of showing relief and elevation on a standard topographic map. A contour line represents an imaginary line on the ground, above or below sea level. All points on the contour line are at the same elevation. The elevation represented by contour lines is the vertical distance above or below sea level. The three types of contour lines (see Figure 9-1) include— Index. Starting at zero elevation or mean sea level, every fifth contour line is a heavier line. These
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  • Fall '16
  • Cartography, Geographic coordinate system, Topographic map, Universal Transverse Mercator coordinate system

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