On topographic maps, lines of longitude indicate North direction or True North.
Magnetic North direction is also indicated on topographic maps. The difference in angle between Magnetic North and True North is called the Magnetic declination. The value of Magnetic declination varies slightly from place to place and time to time. The amount of such variation is also indicated in topographic maps.
Directions are usually measured clockwise from North. If the directions of point A is 225 degrees from B, it means, A is located South West of B. This is a type Whole Circle Bearing.
Sometimes bearings are measured from the North-South line. This is called Quadrantal Bearing. The relation between the two is expressed below:
Whole circle Bearing
Quadrantal Bearing
QA
40°
N 40° E
OB
130°
S 50° E
OC
240°
S 50° W
OD
330°
N 30° W
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