You upload your data and it appears in the middle of the ocean, or shrunk into a tiny corner of the map. Nine times out of ten, the cause is a coordinate system mismatch. You do not need a geodesy degree to fix it — just a few core ideas.
Geographic vs. projected
A geographic coordinate system describes positions on the round Earth using latitude and longitude in degrees. A projected coordinate system flattens the Earth onto a plane and measures in units like meters. Web maps expect geographic coordinates; many GIS datasets arrive projected.
WGS 84 is the web standard
For web mapping, the format to use is WGS 84, known by the code EPSG:4326. It is what GPS uses and what GeoJSON assumes. If your coordinates are small numbers between roughly -180 and 180, you are probably already in WGS 84.
Spotting the wrong system
- Coordinates in the hundreds of thousands or millions usually mean a projected system measured in meters (such as a UTM zone or a national grid).
- Data that lands in the ocean off West Africa points to coordinates of (0, 0) — empty or zero values.
- Data squeezed into one pixel means the units are being read as degrees when they are actually meters.
How to fix it
The cleanest fix is to reproject to WGS 84 before or during upload. If your file carries its coordinate system with it — like a Shapefile with a .prj file or a GeoTIFF with embedded georeferencing — MapDataHub can reproject it for you on upload. For a bare CSV, make sure the lat/long columns are already in decimal degrees.
When someone hands you a dataset, ask one question up front: "What coordinate system is this in?" Knowing the answer saves far more time than guessing after the data lands in the wrong place.