Lesson 5: Mobile Mapping Fundamentals
Author: Nicolas R. Malloy
5.9 Orienteering and Ranging
When collecting data in the field a useful tool to have is a compass. While there are many different types of compasses available on the market, the compass that I will discuss here is the orienteering compass.
The orienteering compass has the following basic components:
- Rotating magnetic needle inside a liquid filled capsule
- Orienteering arrow
- Bezel with azimuth graduations and cardinal directions
- Index pointer
- Clear baseplate with meridian lines
- Declination scale and adjusting key
- Sighting mirror
- Targeting sight
When held in a level position, the magnetic needle floats freely inside the liquid filled capsule. Sometimes one end of the magnetic needle is painted red. This indicates the portion of the needle that points to magnetic north.
The orienteering arrow generally appears as an arrow outline that rotates with the bezel, azimuth graduations, and meridian lines. The north end of the orienteering arrow, sometimes painted red, can be rotated to line up with the northern end of the magnetic needle. The azimuth can then be read just under the index pointer. On a USGS topographic quadrangle, azimuth is determined by aligning the edge of the orienteering compass along a line between two points of interest, then rotating the meridian lines so that they line up with meridians on the map. The adjusting key rotates the declination scale to compensate for local magnetic declination. When determining the azimuth of a distant object the lanyard is used to steady the compass and provide the correct distance from the compass to the eyes of the user.
Navigation Toolbox: Compass bearings by James van Oppen
The targeting sight lines up with the distant object and the sighting mirror is used when rotating the bezel and reading the azimuth.