MSL101L04 Basic Map Reading SR.pdf lesson 4.pdf

# The 1100000 scale lower left in figure 4 16

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The 1:100,000-scale (lower left in Figure 4-16) subdivides the 1000-m grid block into five major subdivisions of 200 m each. Each 200-m block is then divided in half at 100-m intervals. The 1:25,000/1:250,000 (center, lower right in Figure 4-16) can be used in two different scale maps; 1:25,000 or 1:250,000. The 1:25,000-scale subdivides the 1000-m grid block into 10 major subdivisions, each equal to 100 m. Each 100-m block has five graduations; each equal to 20 m. Points falling between the two graduations can be read accurately by using estimation. These values are the fourth and eighth digits of the coordinates. The 1:250,000-scale is subdivided into 10 major subdivisions, each equal to 1000 m. Each 1000-m block has five graduations; each equal to 200 m. Points falling between two graduations can be read approximately by using estimation. LOCATING A POINT USING GRID COORDINATES 4-12. Based on the military principle for reading maps RIGHT and UP, locations on the map can be determined by grid coordinates. The number of digits represents the degree of precision to which a point has been located and measured on a map. More digits mean the measurement is more precise. D ETERMINE G RIDS W ITHOUT A C OORDINATE S CALE 4-13. In order to determine grids without a coordinate scale, the reader refers to the north-south grid lines numbered at the bottom margin of a map. Then read RIGHT to the north-south grid line that precedes the desired point (this first set of two digits is the RIGHT reading). Then, by referring to the east-west grid lines numbered at either side of the map, the map reader moves UP to the east-west grid line that precedes the desired point (these two digits are the UP reading). In Figure 4-17, coordinates 1484 locate the 1000-m grid square in which point X is located; the next square to the right would be 1584; the next square up would be 1485, and so forth. To locate the point to the nearest 100 m, use estimation. By mentally dividing the grid square in tenths, estimate the distance from the grid line to the point in the same order (RIGHT and UP). Give complete coordinate RIGHT, then complete coordinate UP. Point X is about two- tenths or 200 m to the RIGHT into the grid square and about seven-tenths or 700 m UP. The coordinates to the nearest 100 m are 142847.

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Grids 15 November 2013 TC 3-25.26 4-21 Figure 4-17. Determining grids without coordinate point D ETERMINE G RIDS W ITH A C OORDINATE S CALE 4-14. In order to use the coordinate scale for determining grid coordinates, the map user has to make sure that the appropriate scale is being used on the corresponding map, and that the scale is right side up. To ensure the scale is correctly aligned, place it with the zero-zero point at the lower left corner of the grid square. Keeping the horizontal line of the scale directly on top of the east-west grid line, slide it to the right until the vertical line of the scale touches the point for which the coordinates are desired. (See Figure 4-18.) When reading coordinates, examine the two sides of the coordinate scale to ensure that the horizontal line
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• Fall '16
• Cartography, Geographic coordinate system, Topographic map, Universal Transverse Mercator coordinate system

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