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I've downloaded from http://extract.bbbike.org/ a map of the waterways and waterbodies within Greater London, Uk. I've loaded the shapefile into QGIS and opened its attribute table. I see that the first column, titled osm_id, has numbers. I'd like to convert these to OSGB coordinates. I've attached a screen shot of the attribute table and its osm_id column.

enter image description here

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    osm_id is a unique identifier not geometry. use the attribute calculator you may use $x and $y to calculate in qgis this will be lat/lng then convert to osgb36 for GB coordinates
    – Mapperz
    Feb 9, 2015 at 5:02
  • Okay, thanks very much. In the end I extracted the vector nodes and was then able to get the coordinates for each point with vector>geometry tools>export/Add geometry columns.
    – Gavin
    Feb 11, 2015 at 0:46

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A river has more than one coordinate, so I wonder if you want a center coordinate, or the whole river geometry.

You have the latter already in the shapefile. To export the geometry to coordinate points, you can use the MMQGIS plugin.

If you want the center coordinate, create small buffers around the lines, and let QGIS calculate the centroid of those buffer polygons.

Once you have the coordinates, you can save them into any other CRS, and add geometry columns to the attribute table with the coordinate values.

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  • Thanks very much for your comments, and for the MMQGIS plugin tip. I haven't used that before. I decided in the end to extract the vector nodes for the rivers and then get their coordinates by using vector>geometry tools>Export/Add geometry columns. That worked for me. Thanks again.
    – Gavin
    Feb 11, 2015 at 0:50

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