What is a .PRJ file?
The .prj extension is mostly an Esri projection file, but is also reused as a generic project file.
Esri projection (WKT)
- What it is
- An Esri .prj projection file - the coordinate reference system in WKT, stored beside a shapefile. Analyser reads the CRS.
- How to tell it apart
- An Esri .prj is one line of WKT beginning with GEOGCS or PROJCS.
- Did you know
- A shapefile's .prj holds one line of Well-Known Text naming the coordinate system, so software knows whether your numbers are degrees or metres.
- If the .prj is missing, GIS software cannot tell which coordinate system the shapefile uses, a frequent cause of layers landing in the wrong place on the map.
- The Well-Known Text it carries is an Open Geospatial Consortium standard, so the same projection definition moves cleanly between Esri, PostGIS, GDAL and other tools.
Generic project file
- What it is
- A project file for one of many applications - the extension is reused widely. Analyser opens it as text where it can.
- How to tell it apart
- Anything that is not WKT is treated as a generic text project.
- Did you know
- Dozens of unrelated apps grabbed .prj for 'project file', which is why the same extension can mean a map projection or a sound-editor session.
- Microcontroller toolchains such as CodeVisionAVR store their build settings in a .prj that has nothing to do with any map.
- Because the extension states only 'project' and nothing about the contents, the sole reliable way to identify one is the application that made it or its internal header.
- Depth of analysis
- .PRJ is an identification-grade format: Analyser recognises it from its bytes and decodes the header metadata it carries, rather than opening it in a full viewer. Formats that do get a full viewer are marked "Full" on the formats page.
- Open a .PRJ file
- Drag a .PRJ file onto the Analyser home page (or tap to pick one). It is identified entirely in your browser - nothing is uploaded, there is no account, and it works offline once installed.