Land surveying in Indonesia: DGN95, TM-3 and a country of zones
Across an archipelago spanning nine UTM zones, a coordinate without its zone lands in open water.
Field takeaways
- The official datum is DGN95; it practically coincides with GNSS.
- General mapping runs in UTM; the country spans nine zones, 46 through 54.
- The cadastre uses TM-3: narrow 3-degree slices specific to cadastral work.
- Straddling the equator, the country demands care with north/south zone labels.
- The app opens in Indonesia with the official system covering the location.
The official frame: DGN95
Indonesia's official datum is DGN95, practically coincident with modern GNSS measurements. General mapping runs in UTM; the archipelago stretches from zone 46 in the west to 54 in the east. Because the country straddles the equator, the north and south halves of the same zone carry different labels — 49S and 49N are different worlds.
TM-3: the cadastre's narrow slices
Cadastral work uses TM-3 instead of UTM: narrow 3-degree slices specific to the cadastre. A narrow slice keeps local distortion small; the price is more slices, and the obligation to always say which one a file is in. A file from the cadastral office is most likely TM-3; data from national portals is UTM.
Zone discipline
In a nine-zone country the zone is part of the coordinate. The same number pair looks valid in Sumatra and in Papua; only the zone says which is meant. Writing the zone into the file name is not politeness in Indonesian practice — it is a requirement.
What the app does in Indonesia
MapLab Survey opens in Indonesia with the official system covering the location. The national network, UTM zones and TM-3 sit together in the catalogue; conversion between WGS84, UTM, DGN95 and the national network happens in the app. The delivery exports in the project's slice as DXF or CSV.
The practical check
Write a known point in both systems and confirm the difference is of the expected order. The TM-3-UTM difference is systematic; surprises only appear when the zone is wrong.
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 datum is official in Indonesia?
DGN95; general work runs in UTM, cadastre in TM-3 slices.
What is TM-3 and how does it differ from UTM?
Narrow 3-degree slices specific to the cadastre; the narrow slice shrinks local distortion but makes the zone label mandatory.
The country straddles the equator — what needs care?
The N and S labels of the same zone use different false origins; 49S and 49N cannot be mixed.
Which system does the app open with in Indonesia?
The official system covering the location; conversion between WGS84, UTM, DGN95 and the national network happens in the app.
Technical references
The field guidance in this article is aligned with the technical and official references below.
Related: Coordinate conversion app · Placing a scanned sheet · Bluetooth RTK GNSS · MapLab Survey