I am using QGIS to make some boundaries adjustments of the Italian provinces over the years. I have a shapefile with the provincial boundaries in 1961 and another one with the boundaries in 2001. No value is missing in these shapefiles. However, when I use "Union", I get some NULL values. Why does this happen? And how can I handle them?

  • Silvia, what fields are causing the NULL values, can you share a snapshot of the attribute table(s) (both before and joined after)? – JClarkson Feb 13 at 15:05
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    If you are using an overlay layer in the algorithm then I believe the Null values indicate that it does not share any overlapping geometry with the input vectors but I would need to see an example of your inputs and outputs to confirm what is happening. – AWGIS Feb 13 at 15:05

Shapefiles cannot store NULL values since the database is dBase III format. This may just be a default setting in QGIS that represents blank values as NULL. Look under Settings (menu)>Options>Data Sources and remove the NULL value text.

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