Mystery WMATA/Metro survey markers: Can any intrepid city planners or engineers explain what these discs are (or were) used for? I seem them all over the place, even sometimes away from Metro stops.namico2000 t1_j2a3bg5 wrote
Reply to comment by RedTreeDecember in Mystery WMATA/Metro survey markers: Can any intrepid city planners or engineers explain what these discs are (or were) used for? I seem them all over the place, even sometimes away from Metro stops. by LilGeographersRoom
Yes, the exact location of the marker was recorded when it was put in, the X, Y, and Z (elevation) coordinates. They use it as a control to measure from. You might see things like this, which are temporary measuring targets, periodically. They're really important for having a baseline to go from to figure out if things have shifted/moved over time.
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