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I am trying to locate an area that is currently in GML format. I know it is somewhere in Istanbul but I need to know which Coordinate Reference System (CRS) it uses to overlay it with other maps. However, the code does not include the name of the utilized CRS. I added the coordinates of a building from the GML below. Could someone please help me to find out the CRS associated with these coordinates?

<gml:posList srsDimension="3">
    425883.554 4534249.139 46.709 425881.290 4534249.821 47.428
    425877.212 4534247.779 47.835 425883.554 4534249.139 46.709
</gml:posList>

TLDR, I understand that this somewhat resembles UTM Coordinates. Although the North value seems correct for UTM, the East value does not.

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  • The easting values are perfect for UTM: 425k is west of whatever central meridian it is. However, you have to tell us where the data's supposed to be, because these coordinates occur in every UTM zone.
    – mkennedy
    Sep 15, 2023 at 15:52
  • That easting/northing pair is not anywhere near Istanbul according to WGS 84 UTM 35N and other projected CRS. It is in Greece. You can use this tool to verify: epsg.io/… Sep 15, 2023 at 16:13
  • centroid is at lon=40.956026, lat=26.119282 Sep 15, 2023 at 16:20

1 Answer 1

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Use projfinder.com. Stick your coordinates in the box, zoom the map to where you think the point should roughly be, click "Find My Projection" and it scans thousands of projections and sees which ones turn out near the crosshairs on the map.

Here's what I get for your first coordinate pair:

enter image description here

So there's one coordinate system (EPSG: 2320, pale yellow dot) which is in Istanbul, and several variants of UTM 35N (darker yellow dot because overlay) which are well west of Istanbul, just across the border in Greece.

Zooming in on the EPSG:2320 location, its here:

enter image description here

Looking at https://epsg.io/2320 I see its an older code, sir, but it checks out. Based on a 1924 spheroid and a 1950 standard datum. Its meant for mapping in Türkiye, so I reckon this is correct. But only you can tell us by accepting this answer...

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