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:
- Error with the shapefiles.
- Shapefiles are too big.
- The data type of the LENGTH field is inappropriate.
- 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.