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I'm trying to join a field named "Area" belonging to the shapefile 'Ancient Woodland' with the shapefile 'Net Development Area' (see screenshots below). The results only return 'NULL' which I don't understand because the field type of "Area" is a number. Even if I join the entire table to Development area all the entries return 'NULL'

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Both shapefiles have a common field which I'm using to perform the join ("Substations"). Surely I don't need to create a .csvt to do this?

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    Joins on floating-point values are nearly impossible due to representation issues. Just about any database primer will explain this. – Vince Aug 30 '17 at 10:22
  • Hi Vince, not sure what you mean by floating-point values – James B Aug 30 '17 at 10:39
  • which fields are you using to make the join? if none of the columns are present it means the join failed – Ian Turton Aug 30 '17 at 10:41
  • I'm using a field called Substations as a common field across both shapefiles. There are only 73 ancient woodland features versus the 408 features belonging to the Development Area shapefile. I've calculated areas of the dev areas and ancient woodland and named both fields "Area" (both shown at ID 48 in the screenshots above). I want to join Ancient Woodland's "Area" field to the development table. When doing so QGIS changes the field name to "Ancient Woldnad_Area" but all the entries are 'NULL' – James B Aug 30 '17 at 10:47
  • My temporary solution in to save ancient woodlands as a CSV and perform the =VLOOKUP formula in excel with the Net Development Area CSV – James B Aug 30 '17 at 11:13
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Table join doesn't work that way, you need to select two columns that contain the same text for features that you want to join.

So in your case you need to choose Substations in both Join and Target field.

  • Perfect iant, sorry for being ignorant! – James B Aug 30 '17 at 12:11

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