In plane surveying, the distance between two points means the horizontal distance. If the points are at different elevations, then the distance is the horizontal length between plumb lines at the points.

A theodolite is a precision instrument used for measuring angles both horizontally and vertically. Theodolites can rotate along their horizontal axis as well as their vertical axis.

The principle of tacheometer is based on property of isosceles triangles, where the ratio of distance of the base from apex and length of the base is always constant.

One of the main objectives of the surveying is to compute the areas and volumes. Generally, the lands will be of irregular shaped polygons. Under this method the given area is split into two with a base line run at the centre.