Land surveying in Türkiye: TUREF, ITRF and the ED50 legacy
In Türkiye a coordinate means little until you know its slice and its datum.
Field takeaways
- Official production runs on TUREF/ITRF in 3-degree TM slices.
- TM30, TM33 and TM36 are the workhorse slices; TM30 is EPSG 5254.
- Older sheets sit in ED50, metres away from TUREF.
- The WGS84 your GPS gives practically coincides with TUREF — not with ED50.
- The app opens in Türkiye with direct XY display.
The official frame: TUREF and ITRF
Türkiye's official datum is TUREF, tied to the ITRF family. Large-scale production runs in 3-degree Transverse Mercator slices: TM30 (EPSG 5254) with its central meridian at 30, TM33 at 33, TM36 at 36. The same point yields two different eastings in two neighbouring slices; giving a coordinate without naming the slice is giving a street number without the street.
ED50: the old datum still in the field
The European Datum of 1950 underpinned sheet production for decades, and most archived sheets still sit in it. The difference between ED50 and TUREF varies by region and is measured in metres. If a coordinate read off an old sheet is compared with today's measurement without a datum transformation, what looks like drift is usually just the datum gap.
Which one does the phone give?
A GNSS receiver's native output is WGS84, which for practical field work coincides with ITRF/TUREF. So the phone's position agrees with a TUREF sheet and disagrees with an ED50 one. That is the first question to ask before wondering why two sheets refuse to line up.
What the app does in Türkiye
MapLab Survey opens in Türkiye with direct XY display: the official TM slice covering the location is selected and easting/northing values appear on screen. ITRF/TUREF TM and UTM slices, ED50 and WGS84 all live in the same catalogue; conversion happens in the app, and the result exports to DXF, KML or CSV with its slice attached.
One delivery rule
Which slice, which datum — those two facts belong in the file name or the project note. Nobody can misread a CSV labelled "TM30, TUREF"; everybody reads an unlabelled one differently.
Try these steps on your own phone.
MapLab Survey handles RTK/GNSS point capture, drawing, area and volume calculations and coordinate conversion, then exports to DXF, KML/KMZ, GeoJSON, Shapefile, GeoPackage, NCZ or CSV. Capture, calculation and export work offline. Live NTRIP corrections and online basemaps need a connection.
Frequently asked questions
Which coordinate system is official in Türkiye?
3-degree TM slices on the TUREF datum. TM30, TM33 and TM36 carry most large-scale work.
Why does an ED50 sheet disagree with a TUREF measurement?
They are different datums; the gap varies by region and is metre-level. They cannot be compared without a transformation.
Does the phone's GPS coordinate agree with TUREF?
For practical field work yes: WGS84 and ITRF/TUREF are treated as coincident. It does not agree with ED50.
Which system does the app open with in Türkiye?
The official TM slice covering the location, with direct XY display; the catalogue lets you switch.
Technical references
The field guidance in this article is aligned with the technical and official references below.
Related: ED50 to TUREF · Coordinate conversion app · Bluetooth RTK GNSS · MapLab Survey