prj
What is a .prj file?
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A .prj file is the coordinate-reference-system sidecar of an Esri shapefile. It contains a single line of Well-Known Text describing the CRS: for a projected system, the projection method, its parameters, the linear unit, and the geographic system it is based on; for a geographic system, the datum, spheroid, prime meridian, and angular unit. Without it a shapefile's coordinates are just numbers.
How to use a .prj file
Use an example .prj file to test CRS parsers and reprojection pipelines, checking that a WKT definition is matched to the right EPSG code and that the axis order and units are honoured rather than assumed.
Download example .prj files
- Shapefile — Projection Sidecar (.prj, WGS 84)The one-line WKT that tells a reader what the .shp coordinates mean. Esri's flavour uses D_WGS_1984 and GCS_WGS_1984 rather than the OGC names and carries no EPSG authority code, so identifying it means matching the datum and spheroid rather than reading an ID.
- PRJ — WGS 84 Geographic in WKT 1 (Esri flavour)The reference .prj for this category: WGS 84 geographic in Esri's WKT 1 dialect, which uses D_WGS_1984 and GCS_WGS_1984 in place of the OGC spellings and carries no AUTHORITY node. Everything else in this family is a variation on it.
- PRJ — WGS 84 in WKT 2 (2019)The same CRS in WKT 2, which renames almost every keyword (GEOGCRS, ELLIPSOID, LENGTHUNIT) and — crucially — declares axis order explicitly with AXIS and ORDER. WKT 1 left that implicit, which is the root of most latitude/longitude swaps.
- PRJ — Web Mercator (EPSG:3857) in WKT 1The projection every web map uses, defined as Esri's Mercator_Auxiliary_Sphere. It treats the ellipsoid as a sphere for the projection maths while keeping ellipsoidal latitudes, which is why it is a pseudo-Mercator and why it cannot represent latitudes beyond about 85.05 degrees.
- PRJ — UTM Zone 28N (EPSG:32628) in WKT 1The UTM zone that actually contains the invented territory: zone 28N, central meridian 15 W. It is a definition fixture only — no projected coordinates are published for it here, because a transverse Mercator value is not something to take on trust from a fixture.
- PRJ — World Equidistant Cylindrical (EPSG:4087) in WKT 1Plate carrée on a sphere of radius 6,378,137 m — the simplest projection with a closed form you can check by hand. That is exactly why it is here: it makes the reprojection pair in this subcategory verifiable with a calculator rather than a library.
- Convert v2 Shapefile PRJ CompanionReal PRJ component from the five-town Kestrel Bay shapefile set, copied byte-for-byte into the Convert v2 reserve. Stable P8 artifact p8-convert-shapefile-prj.