What is a benchmark?
Geodetic control points are permanently affixed objects at various locations all over the United States to enable land surveying, civil engineering, and mapping to be done efficiently. These objects are usually metal disks, but can be any other object that serves as a control point.
There are two general types of these control points:
- The vertical control point is for precisely establishing the elevation at that point. This type of control point is usually, but not always, a small brass or aluminum disk, concrete post, iron pin, or bolt, (among other things), that is permanently attached to a stable foundation.
- The other general type of control point is for horizontal control. There are several names for horizontal control points - triangulation stations, traverse stations, trilateration stations, GPS stations, and intersection stations, depending on which kind of horizontal control system was used in establishing them and the amount of precision they represent. This type of control point can be a small brass or aluminum disk, concrete post, iron pin, or bolt, (similar to the vertical control points) but also radio towers, water towers, church spires and mountain tops or any other type of object that can be identified from a distance
The City establishes and maintains the vertical control network throughout the City and publishes the current data. 2004 Benchmark book.
Benchmarks are public property and are protected by law. In the unlikely event that you discover a marker lying loose on the ground, leave it where you found it, and contact Survey/Right-of-Way.