Posted & filed under Mapping, Surveying.

When you’re looking at a map, you should have some idea of where you’re starting and where you want to end up. Take that same concept and apply it to surveying, and you’ll understand why it’s so important to select the right benchmark and datum for a survey job.

A “benchmark” isn’t just a slang term for a starting point. It’s an actual, literal mark, usually set in stone or concrete, that’s used as a set place for surveys to take place. It originated from the marks themselves, which can be used to place an actual bench for a leveling rod to sit on. The point of creating an actual mark in that spot is so that surveyors know exactly the height and location from which they’re surveying the land. They also know that every time they set their leveling rod, they’re doing so in the exact same place, which helps in determining any changes to the land.

A “datum” is more abstract. It’s a term that’s used in surveying work to create starting points based on a reference surface, like sea level. They can be horizontal or vertical, measuring locations along the surface of the Earth or measuring land height or ocean depth.

The importance in selecting the right benchmark and datum has everything to do with the type of job. For example, when surveying a floodplain to create a floodplain map, surveyors will want to pay special attention to where sea level is and the height of the land. Using the same benchmark for a series of surveys over time helps engineers get a true sense of whether the land is changing throughout the year, notice whether the earth is shifting, or help insurance providers get a better idea of higher risk planes.

Surveying from the same site and using specific datum measurements means that we can monitor the land to determine erosion, places earthquakes may occur (like fault lines), understand why certain areas are at higher risk of flood, notice an increased danger of mudslides, and much more. By understanding where and when to survey, we can create better construction surveys, property boundaries, levee and dam designs, and ensure our measurements are consistent across the board.

For the best level of accuracy and safety, it’s incredibly important to use benchmarks and datums properly. Doing so allows us to ensure measurements are accurate and provide data that helps keep construction crews and service people safe. An experienced surveyor will know how to use these things to their best advantage.