Surveying

First, benchmarks are located at known latitude and longitude. They are far enough apart from each other that spherical geometry is not accurate enough to compute their distances, and a geoid must be used. The granddaddy of all benchmarks is in Greenwich.

Then, when a plat is drawn, the distance of a control point from a benchmark is given, as well as the location whose north is being used. If the area is less than 400 km², the earth can be treated as flat, but the Cartesian coordinates used in surveying do not match the meridians and parallels except at one meridian.

The standard instrument for surveying is the theodolite.

Modern surveying also makes use of laser theodolites and satellite positioning systems.

Famous surveyors include:

• Liu Hui
• John Ericsson
• Charles Mason and Jeremiah Dixon