I have a polygon shapefile and a (merged) line shapefile (both are zipped). When I use Vector -> Analysis Tools -> Sum Line Lengths on these shapefiles, I get a layer with some of the LENGTHS filled with numeric values. However, a significant portion of the LENGTHS are now 'nan', even when the COUNT is a non-zero value.

Here are a few possible explanations, but I'm not sure which one is correct:

  1. Error with the shapefiles.
  2. Shapefiles are too big.
  3. The data type of the LENGTH field is inappropriate.
  4. I need to unzip them.

I've tried doing the same with a few of the unmerged line shapefiles and this problem still seems to occur.

  • Quick thought - have you checked for any null geometry in your files (and then eliminate any such features)? – MappaGnosis Oct 20 '18 at 9:35

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