I'm trying to join a field named "Area" belonging to the shapefile 'Ancient Woodland' with the shapefile 'Net Development Area' (see screenshots below).

enter image description here

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.

enter image description here

enter image description here

enter image description here

enter image description here

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?

  • 2
    Joins on floating-point values are nearly impossible due to representation issues. Just about any database primer will explain this.
    – Vince
    Commented Aug 30, 2017 at 10:22
  • Hi Vince, not sure what you mean by floating-point values
    – James B
    Commented Aug 30, 2017 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
    Commented Aug 30, 2017 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
    Commented Aug 30, 2017 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
    Commented Aug 30, 2017 at 11:13

1 Answer 1


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
    Commented Aug 30, 2017 at 12:11

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.