By Bryan Richards
Updated Aug 30, 2022
In geography, a horizontal angle is the measurement between two lines that share a common vertex. In topographic surveying, it is typically the angle between two distinct lines of sight. For instance, standing atop a hill, a surveyor may look at two landmarks, and the horizontal angle is the difference between those sight lines.
Horizontal angles are expressed in degrees from 0° to 360°. A right angle equals 90°, and a full rotation is 360°. To record an angle, use a magnetic compass equipped with an outer graduation ring. Align 0° with magnetic north and note the azimuth of each landmark.
1. Point the compass toward the first landmark and record its azimuth (e.g., 0° for north, 180° for south).
2. Repeat for the second landmark.
The horizontal angle is the absolute difference between the two azimuths. Repeat this for every angle you need to average.
Accumulate all measured horizontal angles. If you are collecting daily observations over a month, add the 30 individual readings together.
Divide the total sum by the number of observations. For example, if 30 readings were taken, divide the sum by 30 to obtain the mean horizontal angle.
