In some cases field workers may find it more convenient to tie features and objects, that is map them in reference, to a specific point or benchmark. The benchmark used in any given project can either be an official one established by the government, or one established arbitrarily for that project.
Official benchmarks are usually low concrete monuments capped with an encoded metal plate.
The National Geodetic Survey publishes on CD-ROM a list of all benchmarks and their locations in the United States. An official benchmark can be found on the southeast corner of 24th and Whitis streets on the UT campus. N 30 deg. W 097 deg. A benchmark established arbitrarily for a specific project is known as a datum .