MSL101L04 Basic Map Reading SR.pdf lesson 4.pdf

Make a mark on the map at the desired azimuth remove

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Make a mark on the map at the desired azimuth. Remove the protractor and draw a line connecting the known point and the mark on the map. This is the grid direction line (azimuth). Note. When measuring an azimuth, the reading is always to the nearest degree or 10 mils. Distance does not change an accurately measured azimuth. Figure 6-7. Plotting an azimuth on the map 6-9. To obtain an accurate reading with the protractor (to the nearest degree or 10 mils), there are two techniques to check that the base line of the protractor is parallel to a north-south grid line: Place the protractor index where the azimuth line cuts a north-south grid line, aligning the base line of the protractor directly over the intersection of the azimuth line with the north-south grid line. The user should be able to determine whether the initial azimuth reading was correct. The user should re-read the azimuth between the azimuth and north-south grid line to check the initial azimuth. Note that the protractor is cut at both the top and bottom by the same north-south grid line. Count the number of degrees from the 0-degree mark at the top of the protractor to this
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Directions 15 November 2013 TC 3-25.26 6-9 north-south grid line and then count the number of degrees from the 180-degree mark at the bottom of the protractor to this same grid line. If the two counts are equal, the protractor is properly aligned. DECLINATION DIAGRAM 6-10. Declination is the angular difference between two norths. Having a map and a compass, the declination of most interest is between magnetic and grid north. Soldiers primarily receive information based on a magnetic north or grid north azimuth. The declination diagram shows the angular relationship, represented by prongs among the grid, magnetic, and true norths. While the relative positions of the prongs are correct, they are seldom plotted to scale. Do not use the diagram to measure a numerical value. This value is written in the map margin (in degrees and mils) beside the diagram. Note . Magnetic azimuths are generally used by Soldiers while navigating with a compass or dead reckoning (land navigation). The grid azimuth is generally used by planners and leaders when writing orders, controlling movement, or looking at graphic control measures. 6-11. A declination diagram is part of the information in the lower margin on most larger maps. On medium-scale maps, the declination information is shown by a note in the map margin. Other map information includes: Grid-magnetic (G-M) angle. The G-M angle value is the angular size that exists between grid north and magnetic north. It is an arc, indicated by a dashed line that connects the grid-north and magnetic-north prongs. This value is expressed to the nearest 1/2 degree, with mil equivalents shown to the nearest 10 mils. The G-M angle is important to the map reader/land navigator because azimuths translated between the map and ground are in error by the size of the declination angle, if not adjusted for it.
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  • Fall '16
  • Cartography, Geographic coordinate system, Topographic map, Universal Transverse Mercator coordinate system

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