Systems of Direction

• An observer views the horizon as a circle with himself as the center. Words like north, south, east, and west indicate general direction, but do not provide an accurate description of an object's orientation relative to the center reference point. Map readers use one of two systems of angular measure to accurately determine direction: the degree system and the mil system. A circle consists of 360 degrees. In other words, if the circle was a pie, it would be divided into 360 slices. A degree can be subdivided into 60 minutes, and a minute into 60 seconds. The mil is an angular unit of measure typically used by the military in artillery, tank and mortar gunnery. A circle has 6,400 mils. One degree equals 17.78 mils.
  
  

Principle

• An azimuth is a horizontal angle measured clockwise from a reference line running from a circle's center and pointing north. Because there are 360 degrees in a circle, an azimuth in degrees can be any number between 0 and 360. Due east, south and west are 90 degrees, 180 degrees and 270 degrees, respectively. Due north is 0 degrees or 360 degrees. An azimuth in mils can be any number between 0 and 6,400. Due east, south and west are 1,600 mils, 3,200mils and 4,800 mils, respectively. Due north is 0 mils or 6,400 mils. A protractor determines an azimuth more accurately than a compass.
  
  

Types of Protractors

• A protractor divides a circle into units of angular measure. Types of protractors used for map reading include circular, semicircular, rectangular and square. Each type has a scale around its outer edge, and an index mark at its center from which all directions are measured. The military protractor, known as GTA 5-2-12, is square and has two scales. The inner scale has degree markings and the outer scale has mil markings. Each degree tick mark represents one degree and each mil tick mark represents 20 mils. A common type of protractor is semicircular, made of flat, clear plastic and has degree markings.
  
  

Procedure

• Begin by drawing a straight line, the azimuth line, from the point of origin, point A, to the point of destination, point B. If necessary, extend the line beyond point B so it is long enough to cross the scale of the protractor. Align the protractor's index with one of the map's north-south grid lines through which the azimuth line crosses so that the 0 degree or mil mark is oriented to the north and the 90 degree mark is to the right. Start at the 0 mark and read clockwise to the tick mark where the azimuth line crosses the scale of the protractor. The value determined represents the azimuth.