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"Surveying is the scientific measurement of natural or man-made features of the Earth's surface. On any area of land to be measured, it is always possible to choose 2 points and measure the distance between them, thus creating a line which can be drawn to scale on a map, plan or section. Other points can be located, relative to the line, by taking 2 other measurements, which can also be drawn to scale. These measurements may be 2 angles, one measured line and one angle, or 2 measured lines. From these measurements, a map can be built up with the features accurately located with reference to each other. Surveying is used to make maps of all kinds, to locate buildings and engineering works (eg, dams, bridges, tunnels) accurately, to establish property lines, to chart waterways, and to position such devices as satellites and oceangoing oil-drilling platforms."

From The Canadian Encyclopedia

BPM

This is a cover is for a box that houses a New York City surveying monument. Once the cover is removed there should be a pin with coordinates and elevations.

"Control and topographic surveys are performed to determine the planimetric location and/or elevation of surface or subsurface features, facilities, or utilities. These surveys are normally used to prepare highly detailed site plan maps (and digital databases) of a project site, facilities, or utility infrastructure; for future design, on going construction, or as-built condition. Engineering drawing scales are typically
large--ranging between 1 inch = 30 ft and 1 inch = 100 ft. These surveys are performed over relatively small project sites using tripod-mounted, manually operated, terrestrial survey equipment, such as transits, tapes, levels, plane tables, electronic total stations, and GPS receivers."1

The lettering stands for Borough President Manhattan. Each Borough President's Office houses the Borough's Topographical Bureau, which is responsible for maintaining the borough's official maps, and assigning street addresses. The Topographical Bureau supplies maps, grade studies and a variety of certificates related to building and development.

Thanks to Robert Alvey, Dick Willey and Kevin Willis of the EPA, and Layne Urbas of Roman Stone Construction Company

1: from Department of the Army US Army Corps of Engineers Manual No. 1110-1-1005.