Orienteering

MAPS INTERPRETATION AND USE

Five Colors

Orienteering maps use five standard colors.

Blue - water features like lakes, ponds and streams.

Black - man-made objects or rock features like roads, trails, buildings, cliffs, boulders.

White - open woods you could run through

Green - thick vegetation (light green) or fight (dark green) that you might want to avoid

Yellow - open land, semi-open land, where you can look up and see the sky like fields or power lines.

Brown - land features like earth banks or contours

Scale

Scale refers to the relationship between the size of the map and the actual size of area that is mapped, or relative distance. On a 1:10,000 scale, one of any unit on the map equals 10,000 of the same unit on the ground. Orienteering typically uses "meters" to measure distance.

When you first start Orienteering, one way to simplify scale is to use your thumb to measure the distance between two easy to find points, like the start and end of a parking lot. Then walk that distance and count how many times your left foot hits the ground -- 1 thumb's width equal 80 paces. This gives you an easy way to "eyeball" the relative distance on your map.

GAOC maps use a common scale of either 1:15,000 or 1:10,000. The scale is marked on the map along with a ruler that measures 100 meter increments.

Legend

Orienteering maps use the International Orienteering Federation's standard mapping symbols to describe the details on the map. This information can be found in the map's legend.

Contours

Contour lines and the brown squiggly lines you see on the map. They represent elevation in the landscape. As a beginner, you only need to know that the closer the lines are together the steeper the landscape.

Before the elevation of any point on the map can be determined, the user must know the contour interval for the map he is using. The contour interval measurement given in the marginal information is the vertical distance between adjacent contour lines. To determine the elevation of a point on the map—

Determine the contour interval and the unit of measure used, for example, feet, meters, or yards

Find the numbered index contour line nearest the point of which you are trying to determine the elevation

Determine if you are going from lower elevation to higher, or vice versa. In, point is between the index contour lines. The lower index contour line is numbered 500, which means any point on that line is at an elevation of 500 meters above mean sea level. The upper index contour line is numbered 600, or 600 meters. Going from the lower to the upper index contour line shows an increase in elevation.

Determine the exact elevation of point , start at the index contour line numbered 500 and count the number of intermediate contour lines to point (a). Locate point (a) on the second intermediate contour line above the 500-meter index contour line. The contour interval is 20 meters, thus each one of the intermediate contour lines crossed to get to point (a) adds 20 meters to the 500-meter index contour line. The elevation of point is 540 meters; the elevation has increased.

Determine the elevation of point. Go to the nearest index contour line. In this case, it is the upper index contour line numbered 600. Locate point on the intermediate contour line immediately below the 600-meter index contour line. Below means downhill or a lower elevation. Therefore, point is located at an elevation of 580 meters. Remember, if you are increasing elevation, add the contour interval to the nearest index contour line. If you are decreasing elevation, subtract the contour interval from the nearest index contour line.

Determine the elevation to a hilltop point . Add one-half the contour interval to the elevation of the last contour line. In this example, the last contour line before the hilltop is an index contour line numbered 600. Add one-half the contour interval, 10 meters, to the index contour line. The elevation of the hilltop would be 610 meters.

There may be times when you need to determine the elevation of points to a greater accuracy. To do this, you must determine how far between the two contour lines the point lies. However, most military needs are satisfied by estimating the elevation of points between contour lines

If the point is less than one-fourth the distance between contour lines, the elevation will be the same as the last contour line. In Figure 10-4, the elevation of point a will be 100 meters. To estimate the elevation of a point between one-fourth and three-fourths of the distance between contour lines, add one-half the contour interval to the last contour line.

The contour line immediately below point b is at an elevation of 160 meters. The contour interval is 20 meters; thus one-half the contour interval is 10 meters. In this case, add 10 meters to the last contour line of 160 meters. The elevation of point b would be about 170 meters.

A point located more than three-fourths of the distance between contour lines is considered to be at the same elevation as the next contour line. Point c is located three-fourths of the distance between contour lines. In Figure 10-4, point c would be considered to be at an elevation of 180 meters.

To estimate the elevation to the bottom of a depression, subtract one-half the contour interval from the value of the lowest contour line before the depression. In Figure 10-5, the lowest contour line before the depression is 240 meters in elevation. Thus, the elevation at the edge of the depression is 240 meters. To determine the elevation at the bottom of the depression, subtract one-half the contour interval. The contour interval for this example is 20 meters. Subtract 10 meters from the lowest contour line immediately before the depression. The result is that the elevation at the bottom of the depression is 230 meters. The tick marks on the contour line forming a depression always point to lower elevations..

In addition to the contour lines, bench marks and spot elevations are used to indicate points of known elevations on the map.

Bench marks, the more accurate of the two, are symbolized by a black X, such as X BM 214. The 214 indicates that the center of the X is at an elevation of 214 units of measure (feet, meters, or yards) above mean sea level. To determine the units of measure, refer to the contour interval in the marginal information.

Spot elevations are shown by a brown X and are usually located at road junctions and on hilltops and other prominent terrain features. If the elevation is shown in black numerals, it has been checked for accuracy; if it is in brown, it has not been checked

Orienteering Course

You already learned that the Orienteering course is marked with circles (see Orienteering map), but there are a few more symbols used to mark the Orienteering course:

Triangle marks the location of the start

Double circle marks the location of the finish

Orienting the Map

When you use a traditional road map, you keep it turned so that the writing is face up, like a newspaper. But with an Orienteering map, you orient the map so that the features on the map are lined up with the same features on the ground.

Thumbing

The best way to keep track of where you've been and where you're going is with your thumb. Just fold your map so most of it is out of the way, except for the control your at and the control your going to. Hold your map so your thumb is on top, at your current location. Then move your thumb to your current location as your travel your route to your next control.

In other words...Say you were going from Control 4 to Control 5 in the map above. Since your a beginner, you'll use large land forms to keep track of where you're at. You'll walk along the shore line till you come to an indistinct trail. Move your thumb there on the map. Next you'll go to a stream, a distinct trail and another stream. As you arrive at each of these points, you'll move your thumb to the points on the map.

Compass

The compass is used primarily to orient your map to North. Otherwise, put your compass away and navigate using the map. You don't need to take headings until you get to the Orange course.

Compass use in Orienteering Good compasses have a fluid-filled housing; the fluid dampens the motion of the needle, so that you can use the compass without holding it perfectly still. Avoid inexpensive compasses that do not have fluid-filled housings. The compass needle is painted in two colors. Assuming that the compass is held flat, the red end points to north, and the white end to south. An interesting detail is that there are northern- and southern-hemisphere compasses. This has to do with the fact that the magnetic field lines, to which a compass needle aligns, point into the earth at the north and south magnetic poles. In the northern hemisphere the north end of the needle is pulled downwards, and the south end is counterweighted to balance the needle. When you use a northern hemisphere compass in, say, Australia, the south end of the magnet is pulled downwards by the magnetic field, and is also heavier than the north end - resulting in a needle that catches and drags on the bottom of the compass housing when the compass is held horizontal.

A good compass will last a long time. However, some things can go wrong with a compass: the plastic components can break, or the housing can develop a leak. Over time, the fluid within the housing may turn an opaque blue-green. And, very rarely, the magnetization of the compass needle may reverse, so that the south end now points to north.

Compass use in Orienteering This is a simple skill, and is probably the most important use of the compass:

Hold your map horizontally.

Place the compass flat on the map.

Rotate the map until the "north lines" on the map (a series of evenly spaced parallel lines drawn across the map, all pointing to magnetic north) are aligned with the compass needle.

The map should now be oriented to the terrain. This makes it much easier to read, just as text is easier to read right side up than upside down.

Compass use in Orienteering The most important navigational aid used in orienteering is the human brain. One other navigational device is in allowed and in general use: the compass. Compasses are useful for taking bearings and for orienting the map so that it is aligned with the terrain - but it is possible, in most areas, to complete a course quite easily and efficiently without a compass (an exception: it would be difficult to navigate flat areas poor in prominent features without a compass).

The compass is the only legal navigational aid that can be used in orienteering. Altimeters are specifically prohibited and GPS units are implicitly prohibited by the rules. It has been stated that GPS units could be very useful and helpful aids, but when the question of how an everyday orienteer would use a GPS unit to defeat the reigning US champion in a race was raised, the only valid reply was: "I would wait at the first control for him, use the GPS unit to knock him out, and then proceed on to victory". Technology, however powerful, is no match for basic navigational ability - even in the hands of a good orienteer who is also a technological wizard. Beginning orienteers should learn basic compass skills and work on mastering map reading.