Land Nav Refresher

Lensatic Compass

The lensatic compass is the compass used by the military in field operations. It is simple to use and more accurate than most other simple compasses. It includes a sight, sighting wire and lens to more easily focus on the target and read the dial, luminous features for use in the dark, a thumb ring to hold it steady, and a straight edge for measuring distance on 1:50,000 maps. It folds up for protection, and the rear sight locks the needle, which extends the compass life. The movable bezel ring can be used to preset an azimuth.

What direction do you read a map?

"Right, and Up"

Determine elevation for a point on the map

1. Find the contour interval on the marginal map info 2. Find the nearest INDEX contour and its elevation 3. Determine if you are going lower or higher to the point you are concerned about 4. Count up or down to determine the correct elevation, using the contour interval

3 Types if Azimuth

Magnetic Azimuth: direction expressed as the angular difference between Magnetic North and the direction line (i.e. 140°) Grid Azimuth: the angle measured between Grid North and a line plotted between two points on a map. Back Azimuth: the opposite direction of an azimuth. The back azimuth is 180° from an azimuth. For azimuths more than 180°, subtract 180. For azimuths less than 180°, add 180. A back azimuth of 180° is either 0° or 360

Shooting an Azimuth

1. Turn the dial of the compass to the given azimuth 2. Keep the compass flat in front of you with the "Direction of Travel Arrow" pointing straight ahead. 3. Turn your body so the red (north pointing) needle of the compass lines up inside the red housing on the base of the compass. Once you have the direction, aim on some point in the distance, and go there without staring down at the compass

An 8 digit grid is accurate to __ meters.

10

A 6 digit grid is accurate to __ meters.

100

Map Colors

Black - on a map is the work of humans: buildings, railroads, bridges, boundaries, names Blue - always means water: lakes, ponds, rivers, streams, water well, marshes ... Brown - symbols are used for relief features - contour lines and elevation ... Green - indicates forest, woodlands, orchards, and other areas of heavy vegetation. Red - is used for larger, more important roads and surveying lines. Purple - is for overprinting: Revisions added from aerial photographs but not yet field-checked, or planned additions. White - is mostly clear of trees: fields, meadows, rocky slopes, and other open country.

Supplementary Terrain Features

Cut, Fill Feature where terrain has been cut away - essentially a minor cliff, and where it has been filled in, creating more level ground than would normally be seen on the natural terrain feature. Often done to create a stable platform for a road or railroad.

Supplementary lines

DASHED lines that show one-half the contour interval. They are often used on maps where the contour interval is large, and the terrain somewhat featureless overall

3 Minor Terrain Features

Draw, Spur, and Cliff

Intermediate lines

Four intermediate contour lines fall between the index contours and do NOT show their elevation.

Index lines

HEAVY or DARK colored contours, generally every fifth contour line; they show an elevation number.

5 Major Terrain Features

Hill, Ridge, Valley, Saddle, and Depression

Silva Compass

The Silva Compass, or models like it, is a simple, inexpensive compass that's great for map reading and orienteering. Some have an adjustable baseplate that allows you to adjust for declination, so you can ignore converting grid to magnetic azimuths and back. The compass has direction lines that help align the compass on your map, and assist in pointing along your route. It is not as accurate as a lensatic compass, but works well in an orienteering environment where terrain association is your primary method of finding your way. On a Silva Compass, it's the red part of the compass needle that points north.

Topographic Maps

The feature that most distinguishes topographic maps from maps of other types is the use of contour lines to portray the shape and elevation of the land. Topographic maps render the three-dimensional ups and downs of the terrain on a two-dimensional surface. Topographic maps usually portray both natural and manmade features. They show and name works of nature including mountains, valleys, plains, lakes, rivers, and vegetation. They also identify the principal works of man, such as roads, boundaries, transmission lines, and major buildings.

Grid Zone Designator

This is a 2-letter designation that is unique to a 100,000 meter area. (This is where the grid numbers start over again at 00.) The Grid Reference Box in the Marginal Data shows the Grid Zones that are on that map. The correct depiction of a grid coordinate ALWAYS includes the Grid Zone. i.e. ET 99450076, which is 100,000 meters from FT 9945007

Measuring distance along a road that isn't straight

To measure distance along a road that isn't straight, break up the road into little bits that are more or less straight, measure each leg, and add them together. You can do this on your straight piece of paper by making a tick mark where the road turns, then rotate the paper and make the next tick mark at the next turn. In the end, you have a series of tick marks, but one complete line on your pap

3 types of North

True North is 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 symbolized in marginal information with a star. Magnetic North, as shown by the compass needle, points to the north magnetic pole, which is not the same as the geographic North Pole. It is shown in marginal information as a half-arrow. Grid North is the north that mapmakers put on a map, dependent of the map projection used. It is shown in the marginal information by the letters GN on a vertical line.

Marginal Information

• Sheet Name. Like a title, in the center of the top margin. Also in the lower left margin. • Sheet Number. Listed with the Sheet Name. Used as a reference number for the map sheet. • Adjoining Map Sheets Diagram (Figure 10). Shows the 8 map sheets adjacent to this sheet, with their sheet number (at the same map scale). • Special Notes. • Declination Diagram. Indicates the direction and relationship of True, Grid, and Magnetic North, the G-M Angle, and how to convert grid to magnetic and magnetic to grid. • Scales. Gives the scale used on the map. Graphically depicts distance in miles, meters, and yards. • Contour Interval. Tells you what the vertical distance between contour lines is on this map. • Unit Imprint. Tells you who made the map. • Grid Reference Box. Tells you the 2-digit Grid Zone Designators, and where the boundaries are between grid zones on the map. • Legend (Figure 11). Gives the effective date of the map data and defines the symbols used on the map

To find the grid coordinate of a point:

► Determine the scale of your map. Find the correct scale to use on your protractor. ► Determine the grid square the point is in. This gives 4 digits: 12xx56xx. ► Next, using the correct scale on your protractor, align the bottom right corner of the protractor scale to the bottom right corner of the grid square. ▪ Slide the protractor to the left until the line forming the right edge of the scale intersects the point. ▪ Read off the horizontal and vertical position: ► 4955188