Section 117- Land Nav Flashcards
Discuss the twelve parts of the lensatic compass.
Discuss or show the following:
• True North - A line from any point on the earth’s surface to the North Pole. All lines of longitude are true north lines. True north is usually represented by a star.
• Magnetic North - The direction to the north magnetic pole, as indicated by the north-seeking needle of a magnetic instrument. The magnetic north is usually symbolized by a line ending with half of an arrowhead. Magnetic readings are obtained with magnetic instruments, such as lensatic and M2 compasses.
• Grid North - The north that is established by using the vertical grid lines on the map. Grid north may be symbolized by the letters GN or the letter “y”.
Discuss the techniques used to orient a map using a compass.
Compass
• When orienting a map with a compass, remember that the compass measures magnetic azimuths. Since the magnetic arrow points to magnetic north, pay special attention to the declination diagram.
• With the map in a horizontal position/flat on the ground, take the straightedge on the left side of the compass and place it along the magnetic north (north-south grid lines) arrow on the declination diagram with the cover of the compass pointing toward the top of the map. This procedure places the fixed black index line of the compass parallel to the magnetic north arrow (north-south grid lines).
• Keeping the compass aligned as directed above, rotate the map and compass together until the magnetic arrow is below the fixed black index line on the compass. Your map is now oriented
Terrain Association
• You an orient your map using terrain association when a compass is not available or when you have to make quick references as you move across country.
• Identify prominent terrain features on the map that you can find on the ground.
• Align terrain features with the map. If there is a tower to your front, then orient the map so that the tower is to your right front. If there is a road off to your left, then ensure the road on the map is parallel on the ground.
• Once all of the features are lined up, your map is oriented
Discuss the procedure for determining the location of an unknown point by intersection.
• Intersection is 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. It is used to locate distant or inaccessible points or objects such as enemy targets and danger areas. There are two methods of intersection: the map and compass method and the straightedge method
- Luminous Sighting Dots
- Sighting Wire
- Luminous Magnetic Arrow
- Short Luminous Line
- Fixed Index Line
- Graduated Straight Edge
- Sighting Slot
- Lens
- Thumb Loop
- Floating Dial
- Bezel Ring
- Lens or Rear Sight
Discuss the map features identified by the colors below:
- Red – Classifies cultural eatures, such as populated areas main roads, and boundaries, on older maps.
- Blue - Identifies hydrography or water features such as lakes, swamps, rivers, and drainage.
- Red Brown - The colors red and brown are combined on red-light readable maps to identify cultural features, all relief features, non-surveyed spot elevations, and elevations such as contour lines
- Black - Indicates cultural (man-made) features such as buildings and roads, surveyed spot elevations, and all labels.
- Brown - Identifies all relief features and elevation, such as contours on older edition maps, and cultivated land on red-light readable maps.
Discuss the map features below using a standard 1:50,000 military map:
- Hill - A hill is an area of high ground. A hill is shown on a map by contour lines forming concentric circles. The inside of the smallest closed circle is the hilltop
- Saddle - A saddle is a dip or low point between two areas of higher ground. A saddle is not necessarily the lower ground between two hilltops; it may be simply a dip or break along a level ridge crest. A saddle is normally represented as an hourglass
- Ridge - A ridge is a sloping line of high ground. If you are standing on the centerline of a ridge, you will normally have low ground in three directions and high ground in one direction with varying degrees of slope. Contour lines forming a ridge tend to be C-shaped or V-shaped. The closed end of the contour line points away from high ground
- Depression - A depression is a low point in the, ground or a sinkhole. It could be described as an area of low ground surrounded by higher ground in all directions, or simply a hole in the ground. On maps, depressions are represented by closed contour lines that have tick marks pointing toward low ground
- Finger (Spur) - A spur is a short, continuous sloping line of higher ground, normally jutting out from the side of a ridge. A spur is often formed by two rough parallel streams, which cut draws down the side of a ridge
- Draw - A draw is a less developed stream course than a valley. If you are standing in a draw, the ground slopes upward in three directions and downward in the other direction. A draw could be considered as the initial formation of a valley. The contour lines depicting a draw arc U-shaped or V-shaped, pointing toward high ground
Explain the difference between a grid azimuth, a magnetic azimuth, and a back azimuth.
- A grid azimuth is when an azimuth is plotted on a map between point A (starting point) and point B (ending point); the points are joined together by a straight line. A protractor is used to measure the angle between grid north and the drawn line, and this measured azimuth is the grid azimuth
- The magnetic azimuth is determined by using magnetic instruments, such as lensatic and M2 compasses.
- A back azimuth is the opposite direction of an azimuth. It is comparable to doing “about face.” To obtain a
- Back azimuth from an azimuth, add 180 degrees if the azimuth is 180 degrees or less, or subtract 180 degrees if the azimuth is 180 degrees or more. The back azimuth of 180 degrees may be stated as 0 degrees or 360 degrees. For mils, if the azimuth is less than 3200 mils, add 3200 mils. if the azimuth is more than 3200 mils, subtract 3200 miles
• True North -
The north that is established by using the vertical grid lines on the map. Grid north may be symbolized by the letters GN or the letter “y”.
A line from any point on the earth’s surface to the North Pole. All lines of longitude are true north lines. True north is usually represented by a star.
• Magnetic North -
The direction to the north magnetic pole, as indicated by the north-seeking needle of a magnetic instrument. The magnetic north is usually symbolized by a line ending with half of an arrowhead. Magnetic readings are obtained with magnetic instruments, such as lensatic and M2 compasses.
Discuss the techniques used to orient a map using a compass.
Compass
• When orienting a map with a compass, remember that the compass measures magnetic azimuths. Since the magnetic arrow points to magnetic north, pay special attention to the declination diagram.
• With the map in a horizontal position/flat on the ground, take the straightedge on the left side of the compass and place it along the magnetic north (north-south grid lines) arrow on the declination diagram with the cover of the compass pointing toward the top of the map. This procedure places the fixed black index line of the compass parallel to the magnetic north arrow (north-south grid lines).
• Keeping the compass aligned as directed above, rotate the map and compass together until the magnetic arrow is below the fixed black index line on the compass. Your map is now oriented
Discuss the techniques used to orient a map using a terrain association
Terrain Association
• You an orient your map using terrain association when a compass is not available or when you have to make quick references as you move across country.
• Identify prominent terrain features on the map that you can find on the ground.
• Align terrain features with the map. If there is a tower to your front, then orient the map so that the tower is to your right front. If there is a road off to your left, then ensure the road on the map is parallel on the ground.
• Once all of the features are lined up, your map is oriented
