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.RedTreeDecember t1_j29wro8 wrote
Reply to comment by TorontoNeverSkeets 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
So what do they go back and re-measure where they are at some interval?
namico2000 t1_j2a3bg5 wrote
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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