Working with Coordinate Reference Systems
A coordinate reference system (CRS) defines how coordinates on a flat map relate to locations on the curved surface of the Earth. Different CRSes are optimised for different regions and purposes.
Why non-WGS84 data is common in Australian environmental work
Most Australian government spatial datasets — cadastral boundaries, heritage registers, vegetation maps, infrastructure layers — are distributed in one of the Map Grid of Australia (MGA) projected coordinate systems rather than WGS84 latitude/longitude. MGA is based on GDA94 or GDA2020 and uses zone-based projections optimised for accurate distance and area calculations across Australia.
This means GIS files you receive from a state government, a council, or a heritage authority will often arrive in an MGA zone. TerraSitu handles the conversion automatically.
How TerraSitu handles reprojection
When you import a GIS file that uses a non-WGS84 CRS, TerraSitu:
- Detects the CRS from the file's metadata (
.prjfile for Shapefiles, embedded CRS for GeoPackage, GeoJSON, and GML) - Reprojects all features to WGS84 (EPSG:4326) for storage and display
- Records the original CRS code alongside the layer
The original CRS is never discarded. It is stored so you can export the layer back in the original coordinate system if needed.
CRS badge in the layer panel
If a layer was imported from non-WGS84 data, an EPSG:XXXX badge appears next to the layer name in the sidebar. Hovering over the badge shows the full CRS name. This is a visual reminder that the data originated in a different coordinate system.
Exporting in a different CRS
When downloading a layer from the layer panel, a Export CRS dropdown lets you choose the output coordinate system:
- WGS84 (EPSG:4326) — the default; compatible with all GIS tools
- Original CRS — reprojects back to the CRS the file was imported from
- MGA Zone 54 (EPSG:28354) — covers Western Australia (east), Northern Territory (west)
- MGA Zone 55 (EPSG:28355) — covers Queensland, New South Wales, Victoria, South Australia (east), Tasmania
- MGA Zone 56 (EPSG:28356) — covers eastern Queensland, eastern New South Wales
The download button in the layer sidebar opens this dropdown. Click the Download GeoJSON button to export the file with the selected CRS applied.
Common EPSG codes for Australian work
| EPSG code | Name | Typical use |
|---|---|---|
| 4326 | WGS84 geographic | Web mapping, GPS, interchange |
| 4283 | GDA94 geographic | Legacy Australian datasets |
| 7844 | GDA2020 geographic | Current Australian geodetic datum |
| 28350 | GDA94 / MGA zone 50 | Pilbara, Kimberley |
| 28351 | GDA94 / MGA zone 51 | Northern WA |
| 28352 | GDA94 / MGA zone 52 | Southern WA |
| 28353 | GDA94 / MGA zone 53 | Perth metro, SW WA |
| 28354 | GDA94 / MGA zone 54 | Darwin, eastern NT, central Qld |
| 28355 | GDA94 / MGA zone 55 | Brisbane, Sydney, Melbourne, Adelaide |
| 28356 | GDA94 / MGA zone 56 | Eastern NSW, SE Qld, eastern Vic |
| 7854 | GDA2020 / MGA zone 54 | Same area, updated datum |
| 7855 | GDA2020 / MGA zone 55 | Same area, updated datum |
| 7856 | GDA2020 / MGA zone 56 | Same area, updated datum |
Shapefiles and the .prj file
For Shapefiles, the CRS is stored in a companion .prj file. Always include this when zipping a Shapefile for import. Without it, TerraSitu assumes WGS84, which will produce incorrect positions if your data is actually in MGA or another projected CRS.
Related articles
- Importing GIS data — General import workflow and supported formats
- Importing GeoPackage Files — Multi-layer GeoPackage import