114 LAND NAVIGATION FUNDAMENTALS Flashcards
What is the sheet name of a map based on?
The most prominent cultural or geographical feature, often the largest city.
Where is the sheet name located on a map?
Center of the upper margin and either the right or left side of the lower margin.
What is the purpose of the sheet number on a map?
It serves as a reference number for that map sheet.
Where can you find the sheet number on a map?
Upper right margin and lower left margin.
What does the scale of a map represent?
The ratio of a distance on the map to the corresponding distance on the earth’s surface.
How does a 1:25,000 scale differ from a 1:50,000 scale?
A 1:25,000 scale shows more detail because 1 inch represents 25,000 inches on the ground, versus 50,000 inches for 1:50,000.
Where is the scale located on a map?
Upper left margin after the series name and center of the lower margin.
What does the elevation guide illustrate?
A miniature characterization of terrain with bands of elevation, spot elevations, and major drainage features.
Where is the elevation guide typically found?
Lower right margin.
What does the declination diagram show?
The angular relationships of true north, grid north, and magnetic north.
What additional information is included with the declination diagram?
A note on converting azimuths from grid to magnetic and magnetic to grid.
Where is the declination diagram located?
Lower margin.
What are bar scales used for on a map?
Converting map distance to ground distance, with multiple scales in different units.
Where are bar scales positioned on a map?
Center of the lower margin.
What does the legend identify on a map?
Topographic symbols for prominent features like railroad tracks, buildings, and swamps.
Where is the legend found on a map?
Lower left margin.
Why should you always check the legend when reading a map?
Symbols vary between maps, and checking avoids errors.
What are grid lines on a map?
Straight lines intersecting at right angles, forming a system of squares like city streets.
What are principal digits in grid lines?
Two-digit numbers printed at grid line ends and intervals, used for referencing points.
What size are most grid squares on a military map?
1000 meters by 1000 meters.
What is the basic map reading rule for designating a point?
Read right then up, using vertical then horizontal grid lines.
Why is grid square identification important in map reading?
It allows accurate location of points within a grid square using the read right then up rule.
How precise is a four-digit grid coordinate?
Locates a point within 1000 square meters (a grid square).
What accuracy does a six-digit grid coordinate provide?
Locates a point within 100 meters on a map.
How close does an eight-digit grid coordinate pinpoint a location?
Within 10 meters on a map.
What is true north on a map?
A line from any point on the earth’s surface to the North Pole, marked by a star on the declination diagram.
How can true north be found without a compass?
At night, by locating the North Star, which points to true north.
What is magnetic north based on?
The earth’s magnetic field near the North Pole, indicated by the compass’s north-seeking arrow.
How is magnetic north symbolized on a map?
A line ending with a half arrowhead on the declination diagram.
What defines grid north on a map?
A baseline established by vertical grid lines, often marked with “GN” on the declination diagram.
When is true north primarily used in navigation?
When navigating without a compass.
When do you use magnetic north for navigation?
When planning or following an azimuth with a compass in the field.
When is grid north used in map reading?
When plotting or determining an azimuth on a map with a protractor and vertical grid lines.
What is a hill as a terrain feature?
An area of high ground with sloping sides, shown by concentric contour circles.
How is a ridge depicted on a map?
A series of connected hills near the top, with varying or uniform elevation along its length.
What defines a saddle on a map?
A dip or low point between two higher areas, shown as an hourglass or figure-eight contour shape.
What is a finger or spur terrain feature?
A short, continuous sloping line of higher ground jutting from a ridge or hill, with contour lines pointing away from high ground.
How is a draw identified on a map?
A short, continuous sloping line of low ground cut into a ridge or hill, with contour lines pointing toward high ground.
What characterizes a depression on a map?
A low point or sinkhole surrounded by higher ground, shown by closed contour lines with tick marks pointing inward.
What part of the lensatic compass is the cover?
It protects the floating dial and glass encasement, with a sighting wire and luminous dots for night use.
What is the floating dial in a lensatic compass?
A pivot-mounted dial that rotates freely, containing the magnetic needle, luminous arrow, and scales in mils and degrees.
What scales are on the floating dial?
Outer scale in black denotes mils; inner scale in red denotes degrees.
What is the relationship between degrees and mils?
A circle has 6400 mils or 360 degrees; 1 degree equals 17.78 mils.
What does the glass encasement of the compass contain?
It houses the floating dial and has a fixed black index line.
What is the function of the bezel ring on a compass?
It clicks when turned, with 120 clicks (3 degrees each), aiding night navigation with a luminous line.
What is the thumb loop used for on a compass?
It is attached to the base for holding or securing the compass.
What is the rear sight’s role in a lensatic compass?
It locks the floating dial when opened more than 45 degrees, allowing the dial to float freely.
What does the lens do on a lensatic compass?
It is used to read the floating dial accurately.
What is the rear sight slot used for?
It works with the front sighting wire to aim at objects.
What is the G-M angle in map navigation?
The angular difference between grid north and magnetic north, varying by map.
Why must you convert a magnetic azimuth to a grid azimuth?
To plot it on a map, as compasses measure magnetic azimuths and maps use grid north.
How do you convert a magnetic azimuth to a grid azimuth?
Add the G-M angle to the magnetic azimuth.
What should you do with a G-M angle that isn’t a whole degree?
Round it to the nearest whole degree (e.g., ½ degree rounds up to 1 degree).
Where are conversion instructions found on a map?
In the conversion notes next to the declination diagram.
What does the compass measure when orienting a map?
Magnetic azimuths, requiring attention to the declination diagram.
How do you start orienting a map with a compass?
Place the compass straightedge along the magnetic north arrow on the declination diagram, cover pointing to the top.
What is the final step to orient a map with a compass?
Rotate the map and compass together until the north-seeking arrow is below the fixed black index line.
When is terrain association used to orient a map?
When a compass isn’t available or for quick reference while moving.
What is the first step in terrain association for map orientation?
Identify prominent terrain features on the map and ground.
How do you align a map using terrain association?
Match terrain features on the map to their ground positions (e.g., a tower to the right front).
What is location by inspection on a map?
Determining your position by orienting the map and estimating your relation to prominent features nearby.
When is one-point resection accurate for finding your location?
When you’re on or near a linear feature identifiable on the map and ground, with another prominent feature visible.
What is the first step in one-point resection?
Identify the linear terrain feature you are on or near on both the map and ground.
How do you use a compass in one-point resection?
Sight a prominent feature, read the magnetic azimuth, convert to grid azimuth, then to grid back azimuth.
What do you plot in one-point resection?
The grid back azimuth from the prominent feature until it crosses the linear feature on the map.
Why should a feature be perpendicular in one-point resection?
So the back azimuth crosses the linear feature at a right angle for accuracy.
When is two-point resection preferred over one-point?
When you’re not near a linear feature, as it’s more accurate than estimating distance alone.
How many features are needed for two-point resection?
Two prominent features, at least 30° but not more than 150° apart.
What is the process for two-point resection with a compass?
Determine magnetic azimuths to two features, convert to grid back azimuths, and plot them on the map.
Where is your location in two-point resection?
At the point where the two back azimuth lines intersect on the map.
What final step verifies your position in resection?
Conduct a map inspection to confirm the plotted location matches the ground.
