What is the orientation of the topographic map on the ground? Orientation of a map means giving it such a position in the horizontal plane, in which all directions on it would be parallel to the corresponding directions on the ground, and the top (north) side of its frame faces north.
The presence of a graphic card and a compass makes a person armed in any area, and the ability to use them helps along the way. But no description of the terrain can create the correct idea of it, which gives a topographic map. It is a topographic map that serves as a ground guide when driving on roads and without roads, day and night in unfamiliar areas.
Knowing it and knowing how to use it is necessary for everyone, but especially travelers, tourists, prospectors, geologists, surveyors, and the military. You must be able to compare it with the terrain, but most importantly, be able to navigate the terrain on the map. Orientation using a topographic map or aerial photograph consists of orienting the map, determining its location on it (a standing point) and comparing the map with the terrain.
Orientation of a topographic map in the area along the lines of the area, in the direction of the landmark and the compass, taking into account the magnitude of the magnetic declination.
Orientation of a topographic map is carried out mainly along terrain lines and landmarks. And only where they are not visible or not visible, the map is oriented by compass. Orientation of the map according to terrain lines and landmarks is as follows.
If you are located on a site where there is a straight section of the road, it is recommended that you map the road. To do this, rotate the topographic map so that the image of the road on the road coincides with the direction of the road on the ground, and the image of all other local objects located on the right and left of the road are on the same sides and on the map.
Orientation of a topographic map on the terrain along the road.
The advantage of this method of orienting the map on the road is that it provides speed and accuracy of orientation and does not require corrections. It is the main way to navigate cars and other vehicles..
In a closed (wooded) area, as well as in an area where there are few or no linear guidelines, this method is not acceptable. In this case, the topographic map is oriented in directions to the landmark.
If your location on the map is known (for example, a crossroads, bridge, barrow, etc.), then the map is oriented in the direction of any visible landmark indicated on the topographic map.
Orientation of the topographic map in the area in the direction of the landmark.
To do this, apply a ruler or pencil to two points on the map. The point of our standing is the crossroads in the figure above and the windmill is a landmark. And looking along the ruler, they turn with the map so that the selected landmark is on the line of sight.
Compass orienting a topographic map.
If there is no way to orient the map in the direction of the landmark, then use the compass to orient the topographic map. There are three ways to orient the map by compass.
Method for orienting a topographic map by compass if the magnetic declination for a given map sheet is less than 3 degrees.
If the magnitude of the magnetic declination for a given map sheet is less than 3 degrees, it is oriented by compass without taking into account magnetic declination. In this case, the card is given a horizontal position.
A compass is placed on it along the C – S direction along the meridian (western or eastern frame of the map) so that the letter “C” is in the north of the map and the brake of the magnetic needle is released. Carefully rotating the map with the compass, draw the letter “C” on the compass’s dial at the end of the magnetic arrow – the map is oriented.
Method for orienting a topographic map by compass if the magnitude of the magnetic declination for a given map sheet is more than 3 degrees.
If the magnitude of the magnetic declination for a given map sheet is more than 3 degrees, then the map is oriented according to the compass taking into account magnetic declination. At the same time, everyone does the same as in the first method. But then, by rotating the map, the division on the limb of the compass, which corresponds to the magnitude and sign of the magnetic declination indicated in the border design of the map, is brought under the northern end of the magnetic needle.
The figure below (a) shows the first action – how to correctly install the compass on the card when it is not already oriented. Then the second position of the map (b) is shown when it is rotated so that the northern end of the compass needle coincides with the letter “C” (north) on the limb. In this case, the map is oriented, without taking into account the magnetic declination.
In figure (c), the third and last action is performed, that is, the map is rotated so that the northern end of the compass needle coincides with the number +15 degrees on the compass dial, that is, the corresponding eastern magnetic declination. And if it were western magnetic declination, then the topographic map would have to be rotated as shown in figure (d).
Method for orienting topographic map by compass and vertical lines of a kilometer grid.
Often when working on the ground, a topographic map can be folded so that the sides of its frame are wrapped inside it. In this case, you can use the vertical lines of the kilometer grid to orient the map instead of the side of its frame. On one of which the compass is installed according to the same rules as on the side of the frame.
In this case, to accurately orient the topographic map, set it so that the northern end of the compass needle shows a figure on the compass’s dial corresponding to the magnitude and sign of the correction.
Based on the book “Map and Compass My Friends”.