MSL101L04 Basic Map Reading SR.pdf lesson 4.pdf

# These are known as index contour lines normally each

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Starting at zero elevation or mean sea level, every fifth contour line is a heavier line. These are known as index contour lines. Normally, each index contour line is numbered at some point. This number is the elevation of that line.

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Chapter 9 9-2 TC 3-25.26 15 November 2013 Intermediate. The contour lines falling between the index contour lines are called intermediate contour lines. These lines are finer and do not have their elevations given. There are normally four intermediate contour lines between index contour lines. Supplementary . These contour lines resemble dashes. They show changes in elevation of at least one-half the contour interval. Supplementary lines are normally found where there is very little change in elevation, such as on fairly level terrain. Figure 9-1. Contour lines CONTOUR INTERVALS 9-9. Before the elevation of a point on the map can be determined, the user knows the contour interval for the map being used. The contour interval measurement given in the marginal information is the vertical distance between adjacent contour lines. Use the following procedures to determine the elevation of a point on the map: Determine the contour interval and the unit of measure used; for example, feet, meters, or yards. (See Figure 9-2.) Find the numbered index contour line nearest the point being determined for elevation. Determine if the elevation is going higher or lower. In Figure 9-2, point (a) is between the index contour lines. The lower index contour line is numbered 500, which means a point on that line is at an elevation of 500 m above mean sea level. The upper index contour line is numbered 600, or 600 m. Going from the lower to the upper index contour line shows an increase in elevation. To determine the exact elevation of point (a), start at the index contour line numbered 500 and count the number of intermediate contour lines to point (a). Point (a) is located on the second intermediate contour line above the 500-m index contour line. The contour interval is 20 m (see Figure 9-2), and each intermediate contour line crossed to get to point (a) adds 20 m to the 500-m index contour line. The elevation of point (a) is 540 m; the elevation has increased. To determine the elevation of point (b), go to the nearest index contour line. In this case, it is the upper index contour line numbered 600. Point (b) is located on the intermediate contour line immediately below the 600-m index contour line. Below means downhill or a lower elevation. Therefore, point (b) is located at an elevation of 580 m. If the elevation increases; add the contour
Elevation and Relief 15 November 2013 TC 3-25.26 9-3 interval to the nearest index contour line. If it is decreasing, subtract the contour interval from the nearest index contour line. To determine the approximate elevation to a hilltop without a survey marker, add one-half the contour interval to the elevation of the last contour line. (See Figure 9-2, point c.) In this example, the last contour line before the hilltop is an index contour line numbered 600. Add one-half the contour interval, 10 m, to the index contour line. The elevation of the hilltop would be 610 m.

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• Fall '16
• Cartography, Geographic coordinate system, Topographic map, Universal Transverse Mercator coordinate system

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