I've been given a shape file representing a vegetation map which I now have to modify, merging a number of polygons. When I do this, in almost all cases the merge leaves a number of lines, either attached to one of the polygons or completely isolated. An example of the problem (one of the worst) is illustrated in the following screenshots.
Firstly a section of the shape: https://www.dropbox.com/s/amik6g9cdoqg84b/Screenshot%202014-01-15%2017.42.18.jpg The three polygons to be merged selected: https://www.dropbox.com/s/6gl83y2jwgxvrje/Screenshot%202014-01-15%2017.42.33.jpg The section of the shape after the merge: https://www.dropbox.com/s/f1iem85kidkwkwx/Screenshot%202014-01-15%2017.42.53.jpg And a close-up of the unattached lines left after the operation: https://www.dropbox.com/s/i4rmyi7apcfpgg9/Screenshot%202014-01-15%2017.44.05.jpg In case it is relevant, here are my snap options: https://www.dropbox.com/s/73ky3qgbzk16esj/Screenshot%202014-01-15%2017.44.30.jpg And here is a part of the shape file: https://www.dropbox.com/s/n2asd9urvyd5fc8/merge-test.shp If I had just a few polygons to merge, I could simply eliminate the lines, but the file contains about 500, a large proportion of which must be merged. I imagine the problem is caused by errors in the original polygons, but the errors don't show up on either visual examination or using the verify validity function. Any ideas on what the problem might be and how to resolve it, if possible, eliminating it at the roots by correcting the original shape? Thanks, Sarah. P.S. Let me know if you have problems visualizing the images or downloading the file. -- *Sarah Gregg*
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