Bridge surveying is necessary to locate a site, obtain information for design, and furnish lines and grades for construction. A reconnaissance survey is made at all possible sites. A preliminary survey is made at the best site to establish horizontal and vertical control and to obtain information for the bridge design and construction planning. A location survey is made to lay out the bridge according to the bridge plans. During the actual construction, the surveyor establishes any additional lines and grades required by the construction foreman.
The accuracy of measurements and the number and type of survey markers vary with the degree of precision demanded and the type of construction. Variations may range from hand-level and sketch-board work for a tactical bridge to precise measurements for a prefabricated steel bridge.