Kayak Lake Mead's Map & Compass
Magnetic Compass Basics
Compasses are used for orienting the map, orienting yourself to the map, identifying landmarks, and finding position.
There are three (3) "North's":
- The compass needle points to Magnetic North.
- If a line on the map were to point to the North Pole that would be True North.
- The north we use with the map is Grid North.
Grids are superimposed on the map to give us reference lines. True and Grid North are a not exactly the same but the difference is usually negligible for any navigation we are doing. So, in this course we will just use two north's, Magnetic North and Grid North.
The difference between these two north's is called declination or magnetic declination. Sailors use the term, variation. It is measured in degrees. If the magnetic needle is pointing east of the north-south grid line, declination is called out as, "x number of degrees East". Declination varies throughout the world. Around Las Vegas the declination is about 14deg East.
You will find the declination in the margin information on all USGS maps. Here is an example:
All discussion in this book in regard to compass, map, and declination will only involve an adjustable compass in which declination can be set into the compass. Once that is done; map and compass will be synchronized and all “bearings” will be in reference to the map’s grid.
Bearing vs. Course:
Bearing is the direction to a landmark, measured in degrees. The declination adjustable compass measures the bearing to any landmark on the map OR to any landmark on the ground that you sight.
Course is the direction that you want to hike, run, bike, or paddle.
NOTICE: In this example you cannot see the “hilltop” from where you are standing, but the bearing is 243°, whereas your course might be along the orange dots.
A declination adjustable compass:
To orient the map to the ground:
1. Adjust the compass to local declination, here it is 14°
2. Set North (0°) on the bezel ring to the “read bearing
3. Place the compass anywhere on the map with north to
the top of the map and with the base plate along a North-
South grid line.
4. Without touching the compass; turn the map until the
magnetic needle is centered or “boxed” between the green
declination index lines. Now the map is oriented to north.