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

coordinate systemqgisshapefile

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]]

Best Answer

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?

Related Solutions

[GIS] Converting projection

The shp2pgsql tool is used to load data into PostGIS. It is not meant for transforming projections. The -s flag of the command just tells shp2pgsql the SRID of your source data. It doesn't transform the projection at all. You can reproject it before you load it to PostGIS or after.

To transform the projection before you load it to PostGIS, you can use GIS tools like QGIS or GDAL.

To change the projection after loading the data into PostGIS, you can use the ST_Transform command.

Btw, you have to give the shp2pgsql tool the shape file's actual projection. According to Spatialreference.org, your shape file's SRID is 2154. You might want to import it properly this time, using -s 2154 instead of -s 4326 and then perform the ST_Transform on PostGIS.

Of the two options, I think it would be simpler to convert the file before loading it to PostGIS. That way, you won't have to mess around with the spatial database much.

On Identifying your shape file's projection

Stumbled upon prj2EPSG from after reading this thread. Pasted your definition on it and got the following results:

2154 - RGF93 / Lambert-93
3944 - RGF93 / CC44
3949 - RGF93 / CC49

You might want to investigate those three.

[GIS] QGIS 1.8.0 – Define shapefile as UTM 15 NAD83 Feet

UTM is always in metres, being internationally standardized. The proj string for UTM 15N is:

+proj=utm +zone=15 +datum=WGS84 +units=m +no_defs

So if your data is in feet, create a custom CRS with this string:

+proj=utm +zone=15 +datum=WGS84 +units=us-ft +no_defs

or look for the NAD83 projections of the US state your data is about.

EDIT: To add a custom CRS:

Settings -> Custom CRS
Click on the yellow star to create a new CRS
Enter a name, like UTM15 ft
paste the proj string in the second line
Click on the save button

Best Answer

Related Solutions

[GIS] Converting projection

[GIS] QGIS 1.8.0 – Define shapefile as UTM 15 NAD83 Feet

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