Theodolite is an instrument with which we measure the angle between two points as we observe them from the position we are in. With theodolite we can measure angles formed by the positions of distant objects either in terms of the horizontal and/or the vertical plane. Today’s theodolites have a telescope so that observation is done with more accuracy. Theodolite is an instrument with which, knowing the opposition of two initial point with great accuracy, e.g. the pointed top of a mountain or a lighthouse or another obvious point of land, new point on Earth are defined immediately visible from both of the two initial points. Thus, a triangle is formed, the tops of which are absolutely geographically defined and can be imprinted on paper. From the angles of the first «geodesic triangle» other points are defined, forming new triangles, and so on. Ultimately, this method is used to mark «geodesic triangles» that cover the entire geographical area that interests us, which is transferred to scale on paper, creating in this way the exact map of the area.

The demand of the British Admiralty that all of the ships map the areas they visited, constituted the nautical maps of the British Admiralty more correct and complete, covering the maximum surface of the world. Even today, the maps of the British Admiralty are considered the most accurate and guarantee the safe plotting of the sailing of ships at any point on Earth.