[superfries]

are you thinking of benchmarkers that are embedded in objects that have elevation on them?

[muawiyah]

Maybe "benchmark" ~ the Kensington Stone appears to have a number that is the same as the distance from that point in Minnesota to New Orleans in leagues.

Just guessing the early Spanish surveyors probably didn't have the capability of estimating altitude in prairie land but they could estimate distances North and South with great precision.