Understanding GeoJSON Coordinate Reference Systems (CRS)
GeoJSON is an open standard format designed for representing simple geographical features along with their non-spatial attributes. By default, the official GeoJSON specification (RFC 7946) mandates the use of a single coordinate reference system: geographic coordinates using the WGS 84 datum (EPSG:4326), with longitude and latitude expressed in decimal degrees.
Projected vs. Geographic Coordinate Systems
While WGS 84 is ideal for global web mapping platforms, spatial analysis and localized surveys often require projected coordinate reference systems (CRS) such as UTM (Universal Transverse Mercator) or State Plane Coordinate Systems. Projected coordinate systems translate the curved surface of the Earth onto a flat 2D plane using metric coordinates (Easting and Northing), which enables accurate calculations of distance, area, and angle.
Why Convert GeoJSON Coordinates?
Integrating GIS datasets from different sources often results in CRS mismatches. For example, if you download county GIS layers represented in a local state-plane system (meters) and attempt to overlay them on Web Mercator basemaps like OpenStreetMap or Mapbox, the coordinates will not line up. Converting the GeoJSON CRS to WGS 84 resolves these spatial discrepancies and guarantees correct visual overlay.
GeoJSON Coordinate Axis Ordering
A common pitfall in spatial data conversion is coordinate axis ordering. Standard GeoJSON specifies [longitude, latitude] ordering. However, many coordinate systems and legacy databases define positions as [latitude, longitude] or [y, x]. Our converter automatically standardizes coordinates, ensuring compliance with the GeoJSON standard while performing accurate mathematical projection transformations.
How to Use Custom EPSG Codes
If your coordinate system is not in our pre-selected list, you can search for and add any custom EPSG code. The converter queries the epsg.io database to fetch the exact projection definition, enabling you to transform GeoJSON features from thousands of coordinate systems around the world instantly.