Chapter 12: Direction finding and compasses
Direction by definition can only be determined with reference to something. This reference point, whether it is
some object or some known position, establishes a reference line, sometimes called a baseline, between you
and it. So, direction is measured relative to this reference line.
In its simplest form, direction is determined egocentrically, that is, it’s selfcentered. Imagine a line pointing
out from the front of your body. You go left or right, and you say it according to that. If you want to know the
direction to a distance object, the line from you to that object is called the direction line and you are at the
centre of symbolic clock face 12:00.
Geographical Direction Systems
Direction finding ability improves exponentially when you learn to think geocentrically in terms of a
geographical direction system. In this geographical direction system, as with the clock face, direction is
measured in angular units of circle with north at the top. North is 12:00 basically.
True (or geographical) north is a fixed location on the earth—the north pole of the axis of earth
rotation. A great circle line from any point on earth to the north pole—that is, a meridian—is
known as a true north reference line. So, any meridian can serve as your reference line in
finding true north. It’s valuable to mapmakers and GPS users.
The advantage of using true north to reference direction is that you can find it without using any
special instruments. One of the oldest and most reliable ways to find true north is to locate the
North Star (Polaris). It’s positioned in the northern hemisphere sky less than one degree away
from the north celestial pole.
You can use sun to find the true north. The first step is to find and object that casts a welldefined
shadow on level ground. Next, mark the spot at which the top of the shadow touches the ground.
After waiting 30 minutes or so, mark the spot at which the tip of the shadow. A line drawn
between your two marks is a true eastwest line. Since sun rises in the east and sets in the west,
the shadow travels from west to east. So, your first marking will be the west and second will be
the east. So, with east to your right and west to your left draw a perpendicular line, and top of the
line is your true north.
You can use a watch to find the true north as well. Simply hold the watch horizontally at eye
level, and then turn the watch until the hour hand points to the sun. Now picture a spot on the
dial halfway between the hour hand and 12:00. So, that line is true south and the opposite is the
Grid north is the northerly or zero direction indicated by the datum of the grid used on the map.
It’s purely artificial, established for the convenience of those who use maps to measure or
compute directions. Universal transverse Mercator (UTM) grid system is a standardized
system in which the line of constant easting running from top to bottom is oriented to grid north.
Magnetic North This