How many feet different, is it between the old county vertical datum (BCD) and the new one (NAVD 88)?
A. Due to the differences in the ways the two systems were established, as well as other factors, there is no survey grade conversion that can be applied to convert from one system to another. Where we have established NAVD 88 elevations on the older BCD benchmarks and found differences ranging between 1.5 to 1.9 feet. Based on our observations Baltimore County uses 1.7 feet as the approximate difference between the two systems. A benchmark with a BCD elevation of 100.0 feet would have an approximate NAVD 88 elevation of 98.3 feet.
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