How to Set a Projection in MapServer

MapServer defines coordinate reference systems using PROJ.4 parameters inside a PROJECTION block in the mapfile.

Method 1: Using an EPSG Code

The simplest approach is to reference the EPSG code directly:

MAP
  PROJECTION
    "init=epsg:5255"
  END

  WEB
    METADATA
      "wms_srs" "EPSG:5255"
    END
  END

  LAYER
    PROJECTION
      "init=epsg:5255"
    END
    ...
  END
END

Method 2: Using PROJ.4 Parameters

If the EPSG code is not recognized, specify the PROJ.4 parameters explicitly:

PROJECTION
  "+proj=tmerc"
  "+lat_0=0"
  "+lon_0=33"
  "+k=1"
  "+x_0=500000"
  "+y_0=0"
  "+ellps=GRS80"
  "+towgs84=0,0,0,0,0,0,0"
  "+units=m"
  "+no_defs"
END

Search for any EPSG code on the home page and copy the definition from the MapServer tab.

MAP vs LAYER Projections

• MAP PROJECTION: Defines the output projection (the CRS the map is displayed in).
• LAYER PROJECTION: Defines the source data projection.
• MapServer automatically reprojects layers from their native CRS to the MAP projection.

WMS Projections

When serving WMS, declare supported projections in the metadata:

WEB
  METADATA
    "wms_srs" "EPSG:4326 EPSG:3857 EPSG:5255"
  END
END

Notes

• Each PROJ.4 parameter must be on its own line and enclosed in double quotes.
• MapServer uses the PROJ library — ensure PROJ is installed on your system.
• EPSG files are typically located in /usr/share/proj/.