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First off, I am new to GIS. I am using qgis (1.8.0), and have been given a shapefile containing .shp, .prj, .shx, .dbf, however qgis will not load the .prj file stating an invalid data source. Altering the project properties>CRS to WGS84 Epsg:4326 gives correct latitude for the project but incorrect longitude.

The .prj file reads:

PROJCS["British_National_Grid",GEOGCS["GCS_OSGB_1936",DATUM["D_OSGB_1936",SPHEROID["Airy_1830",6377563.396,299.3249646]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",400000.0],PARAMETER["False_Northing",-100000.0],PARAMETER["Central_Meridian",-2.0],PARAMETER["Scale_Factor",0.999601272],PARAMETER["Latitude_Of_Origin",49.0],UNIT["Meter",1.0]]

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1 Answer 1

up vote 3 down vote accepted

The shapefile format consists of several (at least 3) computer files. To load a shapefile into QGIS you point to only the *.shp. The others are read automatically. QGIS does use the *.prj to determine the coordinate system of the data. From the *.prj you quoted above it seems to be in the coordinate reference system EPSG:27700. Here's the spatialreference.og link to a descriptiojn of that CRS.

Now you should be able to enable "On-the-Fly" reprojection and show this layer in any CRS you choose, such as 4326, as you already did. Why do you think the longitude is wrong?

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