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Archive for the ‘Terrain Association’ Category
Map/Ground Comparison!
Movement by Map/Ground Comparison!
Movement by Terrain Association is quicker, less tedious, more forgiving and fun than is Dead Reckoning (dependent on previous location/computations). However, there will be times during movement by Terrain Association when you will need to stop and confirm your position through either plotted or estimated resection.
Errors made using Terrain Association can be corrected fairly easily because you are comparing what you see on the map with what you find on the ground. But, you must be ever mindful that a map is only a previous picture of the earth’s surface drawn to scale. It may or may not be totally representive of what you’ll find on the ground. Some features, especially man-made/influenced, will change with time.
- Matching the Terrain to the Map using Terrain Features: By observing the map’s contour lines, determine Major Terrain Features (hilltop, valley, ridge, depression, and saddle). From a vantage point, compare what you see on the map with what you should see on the ground.
- Compare Vegetation Depicted on the Map: But, be conscious/mindful that it can change overnight from natural accidents or man-made influences.
- Using the Hydrography: Use in-land bodies of water; their shapes, sizes, and direction of water flow.
- Man Made Features: This is an important part of Terrain Association. You should be familiar with the symbols used; consider the map’s age; but, most important, nothing is permanent – if it can be built, it can be torn down!
This method of ground movement will require not only knowledge but a competency in Map Reading, Compass, and Navigational Skills.
Map Orientation!
Map/Compass/Ground Orientation!
A needed preliminary step to map/ground association is to orient the map with the lay of the land. After orientation, if you plot your location on the map, and while doing it see a hill top 2000 yards to the northwest, you should be able to look up and see that same hill top to your right-front at 2000 yards.
The method used to orient the map with the ground depends on what you’re doing. If all you want is a quick analysis, determine north (compass) and point the top of your map in that direction, and map is generally oriented. But, if you’re intention is to determine/plot directions or azimuths on the map and accuracy is critical, the method used should be exact, deliberate and allow no errors:
- Place the map on a flat surface;
- Open compass and place it (straightedge) parallel with a North/South grid-line.
- Keeping the compass aligned, as directed above, carefully rotate the map/compass (together) until the magnetic arrow is below the fixed black index line of the compass (almost oriented);
- To further compensate for the small Grid/Magnetic (GM) angle change, rotate map and compass in the direction of the magnetic arrow in the declination diagram. Whether movement is right or left, rotate the map/compass that small amount (degree/mils) indicated by the G/M angle. The number of degrees/mils of rotation will be reflected under the fixed index line of the compass.
The map and compass are now oriented in accordance with map’s Declination Diagram.
Does it look that way on the map?
Map/Ground Comparison!
We have already established that the top of the map always reflects North, map’s right: East, bottom: South, and the left (as you look at it) would be West.
Based on the vast information contained in the map, including the many different types of terrain and other features; coupled with your Map Reading/ Land Navigation knowledge and skills, it is fairly simple to start visualizing how the land/terrain must appear in relation to your position on the map.
This, couple with your knowledge of the compass and various land navigational techniques, will assist in your map study and terrain/map association. It should culminate with committed movement on the ground. The key to its success is in preparation; it must be as-slow-as necessary, methodical, and very deliberate.
Major Terrain Feature – Hill!
Map/Terrain Association!
A hill is an area of high-ground. From a hilltop, the ground slopes down in all directions. It is shown on a topographical map by contour lines forming concentric circles.
The inside of the smallest circle is the hill-top. This is sometimes marked with an “x”, including the elevation above sea-level in either feet or meters (Bench Mark).
There are electronic devices available that will give altitude readings instantaneously.
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