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.SeattleCardboard t1_j2aojjj wrote
Reply to comment by Successful-Plate3598 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
You'd have to expand on that. I would say the main use of a survey marker is for a surveyor/contractor/engineer to have as a control point. As mentioned by others it gives you an x,y,z based off of a known datum that you can use as a reference point.
The tree is 100' west of this survey marker and 10' higher. We know that the survey marker is at 10000,10000,100 then the tree would be at 9900,10000,110.
That's an easy example and what I would say is their most common use.
When you reference changing elevation that sounds like a high water mark, which is not what is shown in OPs picture.
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