Getting Started in ARDF

Basic Map Skills

de Dale Hunt WB6BYU es Ken Harker WM5R

ARDF events are conducted on varied, wooded terrain through which competitors must navigate using a map and compass. The maps used are topographic, which means that the maps include contour lines to show the shape and elevation of the terrain. These maps are the same maps used for the sport of orienteering. The International Orienteering Federation (IOF) has defined specifications for five-color maps with five-meter contour intervals and standard map symbology. ARDF competitions should, whenever possible, be held on IOF standard orienteering maps at 1:15,000 scale. Learning to use these maps effectively is not just an important skill to avoid getting lost - it is an important skill that can improve your ARDF results. ARDF competitors should strive to know their location on the map at all times, to know where they want to go on the map, and to be able to plan effective routes to get there quickly.

Orienteering maps are prepared to show details of the terrain that humans can easily distinguish as they traverse the terrain. This includes the shape and elevation of the terrain, trails and roads, clearings, fences, overhead power lines, and water features such as streams, rivers, and lakes. Forest is designated on the map based on how difficult it is to traverse. "Runnable" forest, where one could jog or run easily between trees, is distinguished from "slow run," "difficult," and "fight" vegetation. "Fight" refers to vegetation that is so dense that it is almost impassable. Orienteering maps can also mark areas of undergrowth or "rough open." Smaller terrain features can also be marked, such as rock walls, earth banks, distinct boulders, distinct trees, rootstock, and small depressions and pits. Man-made features such as buildings, ruins, wells, hunters' stands, and towers all have map symbols. ARDF competitors should familiarize themselves with the map symbols by reading the IOF Drawing Specifications for Orienteering Maps.

There are some features to orienteering maps that distinguish them from more general-purpose topographic maps, such as USGS maps popular with hikers. The most obvious feature is the magnetic north lines. These are parallel, straight lines, in either blue or black, with arrow heads at the end of the lines that point at magnetic north. Why magnetic north and not true north? The angle between true north and magnetic north (the declination) can be very different in different parts of the world, and can even change subtly over time. It is far easier for mapmakers to draw the lines to magnetic north than it would be to make every individual competitor compensate for the declination in their compass use. As a result, a radio orienteer from Texas can travel to Sweden or China and doesn't need to know how to compensate for the different declination. Their compass and their maps will both be relative to magnetic north.

Orienteering maps will also demarcate the competitive area, and may indicate areas of the map that are "out of bounds." These "out of bounds" areas may be personal residences, a hillside being used for botanical research, a graveyard, or an area under construction. Usually, at a competitive meet, course setter's notes will be available to explain why areas are "out of bounds." Most course setter's notes will also indicate the "safety bearing" for the map. A safety bearing is a direction in which someone who is lost can travel and eventually reach an obvious map feature. For example, if a highway is the eastern boundary of the map, anyone who gets hopelessly lost on course can walk east until they reach the highway. Roads or large water features (rivers, lakes) are the most common features used for a safety bearing.

Compasses

A typical orienteering compass has a clear plastic or acrylic plate with a straight edge underneath the needle housing. The plate often has parallel straight line marked on it and an arrow pointing in the direction of the long end of the plate. This is referred to as a baseplate or protactor compass. The needle housing is filled with a clear fluid that helps dampen the motion in the needle. The best orienteering compasses use proprietary fluids that help the needle settle quickly when the compass is moved, and keep the needle steady even when your hand is not. The needle housing on a baseplate or protractor compass can be rotated, and usually has an arrow marked on the housing below the needle. A variation on this basic design is a thumb compass, designed to be worn on a thumb with an elastic loop, leaving the hand free to hold other items.

It might surprise some people to learn that orienteering compasses are specifically manufactured for use in the northern hemisphere or the southern hemisphere. A northern hemisphere compass is built with a needle that is slightly heavier at its south-pointing end than its north-pointing end. This counters the needle's natural tendency to point down through the earth toward the stronger magnetic pole. Southern hemisphere compasses, where the south magnetic pole is stronger, are built with needles that are slightly heavier at their north-pointing end than their south-pointing end. Without these compensations, the needle would not float as freely in the needle housing when the compass is held horizontally.

Navigating with an Orienteering Map

Most navigation on an orienteering map can be done without any compass use at all. You do not need a compass to follow trails or roads, to follow the track of a stream or gully, or to run to the top of a well-defined hill. Often, you can mark a bearing to an transmitter on the map, and plan a route that uses trails or roads to get you close to the general area of the transmitter. You may find that once you get close enough to the transmitter to leave the trail, you can more or less walk in a straight line until you reach the transmitter.

There may be times, though, when you need to cross sections of forest where you would like to end up at a particular location. Orienteering baseplate compasses make this easy. Place the compass on the map so that the straight edge of the plate is over your present location and the location to which you want to go and the arrow on the baseplate points toward the destination. Rotate the needle housing until the lines underneath the needle housing are parallel to the magnetic north lines on the map (make sure that the arrow on the bottom of needle housing is going in the same direction as the arrows on the magnetic north lines on the map!) Take the compass off the map and hold it in front of you. Rotate your body until the needle lines up with the arrow on the bottom of the needle housing. When you reach this point, the arrow on the baseplate is pointing in the direction you want to go. As you walk or run through the woods, keeping the needle lines up with the arrow on the base of the needle housing is a lot easier than trying to remember that the compass needle needs to point at (for example) 323 degrees.

Most orienteers find that holding the map so that their direction of travel is at the top is easier to use than holding the map with north always at the top. This is, of course, a matter of personal preference. Radio orienteers often need to mark on the map, so having the map fixed to a lightweight but stiff board is also helpful.

 

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Last updated: 19 August 2014
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