Determining the area of geometric figures is an important task performed by professionals involved with Geomatics. Almost all civil engineering projects require calculating the area of a land surface or a geographical or designed feature element. In this sense, although almost all current software applied to Geomatics have modules dedicated to the calculation and division of areas in a CAD environment, this chapter presents the best-known methods of estimating and dividing areas. However, it is important to note that, for legal and administrative purposes, the area of a land surface is generally calculated according to the horizontal projections of the boundary lines that delimit it on the local horizontal ground plane, which is different from the area generated from slope distances or map projections. However, there are design situations where it is necessary to calculate the surface areas represented in a map projection. This chapter only deals with the area calculation of flat surfaces in the local horizontal ground plane.