[GIS] Why is .prj file not being retrieved by QGIS

coordinate systemqgis

My issue is closely related to:

and somewhat similar to:

but it seems that the root of the problem is different.

I am downloaded a shapefile (and all its necessary additional files) from a government repository. When I load the shapefile into QGIS, the CRS is not automatically detected even though a .prj file is in the folder.

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How can I tell QGIS : "please look here and use this .prj file."

DETAILS:

Despite indicating that they use a standard projection (Canada_Albers_Equal_Area_Conic, ESPG: 102001), it actually seems to be a custom projection with a slight tweak to that standard so I can't just choose a CRS from the menu. [If I select "Canada Albers Equal Area Conic", then the polygons are displaced relative to where they should be based on other files for which I know the projection is correct]

The .prj file looks like this:

PROJCS["Canada_Albers_Equal_Area_Conic",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",
SPHEROID["GRS_1980",6378137.0,298.257222101]],
    PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],
    PROJECTION["Albers"],PARAMETER["False_Easting",0.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",-95.0],
    PARAMETER["Standard_Parallel_1",49.0],PARAMETER["Standard_Parallel_2",77.0],PARAMETER["Latitude_Of_Origin",49.0],UNIT["Meter",1.0]]

When I load the file in R, the projection is automatically detected correctly:

> crs(test)
CRS arguments:
 +proj=aea +lat_1=49 +lat_2=77 +lat_0=49 +lon_0=-95 +x_0=0 +y_0=0
+datum=NAD83 +units=m +no_defs +ellps=GRS80 +towgs84=0,0,0

To compare with standard Albers:

CRS arguments:
 +proj=aea +lat_1=50 +lat_2=70 +lat_0=40 +lon_0=-96 +x_0=0 +y_0=0
+datum=NAD83 +units=m +no_defs +ellps=GRS80 +towgs84=0,0,0

If I compare the output provided by the http://epsg.io/102001 website (suggested in an answer), I get the following for the OGC WKT (standard way of writing projections?) for the standard Canada Albers projection:

PROJCS["Canada_Albers_Equal_Area_Conic",GEOGCS["GCS_North_American_1983",DATUM["North_American_Datum_1983",SPHEROID["GRS_1980",6378137,298.257222101]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Albers_Conic_Equal_Area"],PARAMETER["False_Easting",0],PARAMETER["False_Northing",0],PARAMETER["longitude_of_center",-96],PARAMETER["Standard_Parallel_1",50],PARAMETER["Standard_Parallel_2",70],PARAMETER["latitude_of_center",40],UNIT["Meter",1],AUTHORITY["EPSG","102001"]]

And the following as the ESRI WKT way of writing the projection:

PROJCS["Canada_Albers_Equal_Area_Conic",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137,298.257222101]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Albers"],PARAMETER["False_Easting",0],PARAMETER["False_Northing",0],PARAMETER["central_meridian",-96],PARAMETER["Standard_Parallel_1",50],PARAMETER["Standard_Parallel_2",70],PARAMETER["latitude_of_origin",40],UNIT["Meter",1]]

I am noticing slight differences in the language/terms used to set the projection.

Best Answer

The problem is that the .prj is not standardized. You can have several slightly different definitions. For example is the datum value for your EPSG in OGC WKT "North_American_Datum_1983" and in ESRI WKT "D_North_American_1983". Depending on the used program it matches the inbuilt list of defintions or not. It is a well known porblem of QGIS that it often does not recognize .prj that were created by ESRI products.

You can solve it by writing the .prj with QGIS (save as) or by copying the defintions from one of the many EPSG sites like http://epsg.io/102001 . Also QGIS uses its own file .qpj for coordinate reference.

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