Coordinate systems & projections
How DropMaps handles CRS — everything works in WGS84, your original projection is recorded, and exports can reproject back to it.
DropMaps works in WGS84 (EPSG:4326) everywhere — it’s the coordinate system web maps are built on. Whatever projection your data arrives in, DropMaps reprojects it to WGS84 so every layer lines up on the same map.
On import
- Data in a projected or national grid is reprojected to WGS84 automatically (via proj4 / GDAL).
- The layer’s original CRS is recorded and shown in the layer’s Details panel, so you always know what the data started as.
How the original CRS is determined depends on the format:
| Original CRS… | Formats |
|---|---|
| Read from the file | Shapefile (.prj), File Geodatabase, GeoPackage, FlatGeobuf, GeoTIFF / COG |
| You choose it | CSV (pick the EPSG code when your columns are eastings/northings) |
| Assumed WGS84 | GeoJSON, KML / KMZ, GPX, TopoJSON, GeoParquet — these formats are defined as WGS84 lat/long |
If you have a GeoJSON, KML or GPX that is not actually in WGS84, DropMaps can’t detect that and the data won’t line up. Convert it to WGS84 (or to a format that carries its CRS, like GeoPackage or FlatGeobuf) before importing.
The limitation to know about
Because everything is stored internally in WGS84, exporting or downloading a layer “in its original CRS” reprojects it back from WGS84 — a round trip. The result is accurate to normal projection precision, but the coordinates are not guaranteed bit-for-bit identical to your original file.
For day-to-day mapping this difference is invisible (sub-millimetre). But if you need the exact original coordinates — for legal surveys, precise control points, or re-importing into a system of record — keep your authoritative source file; don’t treat a DropMaps round trip as a substitute.
On export
The Export dialog offers “Export in original CRS” when a layer has a real (non-WGS84) source CRS. It reprojects the data back to that projection for GeoJSON, GeoPackage, File Geodatabase, Shapefile, FlatGeobuf and CSV. KML always stays WGS84 — that’s part of the KML standard. With the option off, every export is plain WGS84.
With the QGIS plugin
Cloud layers are stored in WGS84, and the QGIS plugin reprojects each download back to its original CRS (v1.0.5 and later) so it opens in QGIS in the projection it came from. Two things to note:
- Layers uploaded before original-CRS recording was added need to be re-imported into the web app once, so their CRS is captured.
- The reprojection back to the original CRS is the same round trip described above.