Army Board - Land Nav FM 3-25.26 Part 4
This deck covers key concepts from military land navigation, including types of north, azimuths, and methods for determining location on a map.
What are the most common "Norths" used on a military map?
1) Grid | 2) Magnetic
Key Terms
What are the most common "Norths" used on a military map?
1) Grid | 2) Magnetic
What is true north?
A line from any point on the earth's surface to the North pole. (longitude lines) True north is usually represented by a star.
What is magnetic north?
The direction to the north magnetic pole as indicated by the north seeking needle of a magnetic compass. Magnetic north is usually symbolized by a ...
What is grid north.
The north which is established by using vertical grid lines on a map. Grid north may be symbolized by the letters "GN" or the letter "Y"
What is an azimuth?
Horizontal angle measured clockwise from a north baseline. the azimuth is the most common military method to express direction.
How do we obtain a back azimuth?
Add 180 degrees ( if azimuth is 180 or less) | SUBTRACT 180 degrees ( if azimuth is 180 or more)
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| Term | Definition |
|---|---|
What are the most common "Norths" used on a military map? | 1) Grid | 2) Magnetic |
What is true north? | A line from any point on the earth's surface to the North pole. (longitude lines) True north is usually represented by a star. |
What is magnetic north? | The direction to the north magnetic pole as indicated by the north seeking needle of a magnetic compass. Magnetic north is usually symbolized by a line ending with half of an arrow head. |
What is grid north. | The north which is established by using vertical grid lines on a map. Grid north may be symbolized by the letters "GN" or the letter "Y" |
What is an azimuth? | Horizontal angle measured clockwise from a north baseline. the azimuth is the most common military method to express direction. |
How do we obtain a back azimuth? | Add 180 degrees ( if azimuth is 180 or less) | SUBTRACT 180 degrees ( if azimuth is 180 or more) |
What is a magnetic azimuth? | It is determined by using magnetic instruments such as lensatic and M2 compasses. |
What is a grid azimuth? | A protractor is used to measure the angle between grid north and the drawn line. This measure azimuth is the grid azimuth. |
What are the four different protactors. | 1) Full Circle 2) Half Circle 3) Square 4) Rectangle |
What does the declination diagram display? | The angular relationship represented by prongs between magnetic, grid, and true north. |
What is the grid magnetic angle? | The GM angle value is the angular size that exists between Grid and Magnetic north. |
What is the grid convergence? | An ark indicated by a dashed line connecting the prongs for true north and grid north. The value of the angle for the center of the sheet is given to the nearest full minute with it's equivalent to the nearest mil. |
What is the conversion between magnetic and grid north? | There is an angular difference between grid and magnetic. Since location of mag north doesn't correspond exactly with the grid north lines, a conversion from magnetic to grid or vice versa is needed. |
What is the intersection? | The location of an unknown point by successively occupying at least two ( preferably three) known positions on the ground and then map sighting on the unknown location. |
What are the two methods for intersection? | 1) the map and compass method | 2) the straight edge method |
When is the straight edge method used? | When a compass is not available. |
What is resection? | The method of locating one's position on a map by determining the grid azimuth to at least two well defined locations that can be pinpointed on a map. |
When using resection, what method can give you greater accuracy? | To use THREE or MORE well defined locations. |
What is modified resection? | The method of locating one's position on the map when the person is located on a linear feature on the ground such as a road, canal, or stream. |
What are the ways to determine your location on a map? | Intersection, resection, modified resection |
What is the most common and simplest instrument for measuring direction? | The Lensatic Compass |
When is the compass to cheek technique normally used? | For sighting |