Understanding Coordinate Reference Systems (CRS)
What CRS is, why it matters, and how to find the right EPSG code for your data.
Updated April 2026
A Coordinate Reference System (CRS) tells your GIS software what the numbers in your file actually mean — where on Earth they are.
Without a CRS, coordinates are just numbers. With one, (-94.1, 36.3) maps to a specific point in Northwest Arkansas.
Geographic vs Projected CRS
Geographic CRS (like WGS 84 / EPSG:4326) uses latitude and longitude in decimal degrees. It describes position on an ellipsoid model of the Earth. Good for global data and web mapping.
Projected CRS (like UTM, State Plane) converts the curved Earth surface to a flat 2D plane using a mathematical projection. Necessary when you need accurate distance or area calculations.
WGS 84 (EPSG:4326): longitude, latitude in degrees
UTM Zone 15N (EPSG:32615): easting, northing in meters
EPSG codes
Every CRS has an EPSG code — a numeric ID from the EPSG Geodetic Parameter Dataset. These are the standard way to identify CRS unambiguously.
| EPSG | CRS | Common use | |------|-----|-----------| | 4326 | WGS 84 | Web mapping, GPS, GeoJSON | | 3857 | Web Mercator | Tile-based map backgrounds | | 32614 | UTM Zone 14N | US central states | | 4269 | NAD83 | US federal datasets |
Why CRS detection matters
Many files — especially older Shapefiles — have missing or incorrect .prj files. geodata.plus automatically detects the CRS on upload and lets you override it before conversion if detection is wrong.
Use the CRS Validation Preview to confirm: your data should appear in the right location on the map before you convert.