GISMerge requires assert turned off (line 901:shapefile.py)

[gkc1000]

I don't think we can just leave this off. For things to try and check, see comments at: http://geospatialpython.com/2011/02/merging-lots-of-shapefiles-quickly.html

The meaning of the fields is described here in the documentation here:
https://github.com/GeospatialPython/pyshp

For field length, it says "Field length: the length of the data found at this column index. Older GIS software may truncate this length to 8 or 11 characters for "Character" fields."

The assertion error was, I believe, related to one of the fields being "11" (though not sure). One should look through the fields and their meanings more carefully, I think.