What you need
A Shapefile is really several files that belong together:
- .shp — the geometry (required)
- .dbf — the attribute table (names, IDs, …)
- .prj — the coordinate system; needed to reproject correctly
- .cpg — the text encoding of the attributes (optional)
Either select them all at once in the file picker, or put them in a .zip first (most downloads already come zipped). A zip may contain several shapefiles; all of them are imported.
Coordinate systems
GeoJSON uses longitude/latitude on WGS84. If the .prj describes another system — UTM, a State Plane zone, British National Grid, Web Mercator… — coordinates are reprojected automatically. Without a .prj the coordinates are read as they are, and the validator warns you if they don't look like degrees.
Limits
- Z values (PointZ, PolygonZ, …) are kept as a third coordinate; M values are dropped.
- Very large shapefiles (hundreds of thousands of vertices) work but make the map slower; the converter still exports them.