In order to use OTF projection, either your data must contain information about its coordinate reference system or you will need to define a global, layer or project-wide CRS. For PostGIS layers, QGIS uses the spatial reference identifier that was specified when the layer was created. For data supported by OGR, QGIS relies on the presence of a recognized means of specifying the CRS. In the case of shapefiles, this means a file containing the well-known text ( WKT) specification of the CRS. This projection file has the same base name as the shapefile and a .prj extension. For example, a shapefile named would have a corresponding projection file named .