The Westchester County Control Survey conducted ca. 1934-1941 mapped boundary lines throughout the county through use of a triangulation survey. Subjects of the photographs found in this collection include survey equipment, individuals involved in the project, the construction of survey towers, and views from some of the survey stations. A 1939 Control Survey report provides a short history of the project; details with words and photographs the work of the field and office crews involved in the project; and explains the triangulation process used to establish the horizontal grid of elevations throughout the county resulting from the survey, which continue today to serve as “known points” to surveyors mapping property. The report also lists every individual from the county involved in the Control Survey project. Please contact the Archives for additional information on how to access this report and additional records from the Control Survey project.