9.5 Describing Elevation

9.5 Describing Elevation

To describe property located above or below the earth’s surface—such as the air rights of a condominium or subsurface rights—a surveyor must know the property’s elevation.

• Datum: A standard elevation reference point established for an area. The original U.S. datum is mean sea level at New York harbor. Local datums might be, for example, 100 feet above sea level; all elevations are measured above or below this point.
• Benchmark: A local, registered elevation marker used as a reference for nearby properties. Benchmarks simplify surveying by providing a practical, accessible elevation point.
• Once a benchmark is registered, it provides a valid reference for describing elevations in the immediate area.

Why it matters: Elevation descriptions are essential for properties with air rights (such as condos), underground utilities, tunnels, or mining rights.

Check-In Question

• What is a benchmark in property surveying?
  A local, registered elevation marker used as a reference point
  A legal description method
  A type of property boundary
  A point on the property where construction begins
  Show Answer

  Correct Answer: A local, registered elevation marker used as a reference point
  Benchmarks help surveyors accurately describe elevation for properties in the area.