What are permanent metal plates throughout cities in the U.S. used for?

Permanent metal plates, commonly referred to as survey markers or benchmarks, are primarily used for deriving elevation heights. These markers provide a stable reference point for surveying purposes, allowing surveyors to accurately measure changes in elevation and ensure that any construction or engineering work is done to the correct specifications. They are strategically placed throughout cities to assist in mapping and land development projects by providing a reliable and consistent measurement of the earth's surface.

While property taxes and boundaries are related to land use and ownership issues, surveying markers focus specifically on height and elevation calculations. Similarly, while surveying land for development is indeed a broader activity that includes various tasks, the specific role of these metal plates is uniquely tied to establishing elevation references rather than defining boundaries or calculating taxes.