Survey Monument at Coit Tower
A survey monument at Coit Tower in San Francisco. January 2009. This monument was placed by the U.S. Coast and Geodetic Survey agency in 1954.
I was about to label this as a benchmark, but that is not correct. Benchmarks are survey monuments of highly precise elevation, used to measure and survey elevation or height above mean sea level. But this is a horizontal control station, used to survey / establish horizontal locations (latitude and longitude, or other systems of x and y coordinates) on the Earth's surface.
This disk station is named "PLAZA" and "HT3075". You can get detailed data on this survey marker from NOAA's National Geodetic Survey data. Try this link: www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=HT3075
Looking at the data sheet may give you some idea of how this station is used in mapping. From this point, angles to other visible survey markers are precisely measured with survey equipment. Through triangulation and other mathematical calculations, precise locations of the network of control points is determined. The datasheet shows other nearby survey points that were used in this way, including the Alcatraz lighthouse, the north and south piers of the Golden Gate Bridge, points on the Bay Bridge and Treasure Island, a point on the Ferry Building, a beacon on a breakwater in Berkeley, etc.
Survey Monument at Coit Tower
A survey monument at Coit Tower in San Francisco. January 2009. This monument was placed by the U.S. Coast and Geodetic Survey agency in 1954.
I was about to label this as a benchmark, but that is not correct. Benchmarks are survey monuments of highly precise elevation, used to measure and survey elevation or height above mean sea level. But this is a horizontal control station, used to survey / establish horizontal locations (latitude and longitude, or other systems of x and y coordinates) on the Earth's surface.
This disk station is named "PLAZA" and "HT3075". You can get detailed data on this survey marker from NOAA's National Geodetic Survey data. Try this link: www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=HT3075
Looking at the data sheet may give you some idea of how this station is used in mapping. From this point, angles to other visible survey markers are precisely measured with survey equipment. Through triangulation and other mathematical calculations, precise locations of the network of control points is determined. The datasheet shows other nearby survey points that were used in this way, including the Alcatraz lighthouse, the north and south piers of the Golden Gate Bridge, points on the Bay Bridge and Treasure Island, a point on the Ferry Building, a beacon on a breakwater in Berkeley, etc.