For the purposes of land or coastal navigation, a position circle can be generated by making a horizontal angle measurement between two landmarks using a sextant.
When a horizontal angle measurement is made between two known points on land, the observer will be located at the apex of a triangle, with the other two corners of this triangle consisting of the landmark pair.
The observer will also be sitting on a set of points that fall along a large circle.
At each point along this circle, the angular separation between the landmark pairs will be the same.
After the observation is made, the angular reading can be transferred onto a nautical chart (or map) by means of a protractor instrument.