Combining corner-touching polygons into a single feature
I can think of a few approaches that might be worth a try depending on what your data are (they will result in small changes):
- Did you have 'generalise polygons' switched on when you converted from raster to poly?
- You could change the resolution of your raster and use a conservative setting on one of the tools like Boundary-Clean or Nibble before converting to polygons (by up-sampling the resolution, it makes zero effect on the original areas but reduces the size of the change in the final data - you may not feel this is a concern depending on your data)
- You could buffer by a tiny amount (just bigger than your cluster tolerance).
I'm sure there are some other approaches, but I'm running out of steam this evening. Hope these ideas help.
The polygons you are attempting to merge need to share more than one vertex. You cannot dissolve and explode because the polygons that only share one vertex will be separated as well. If you merge the circled groups manually they will become multigeometry as they are not actually intersecting. @Sylvester suggested generalizing when converting as well as other methods. You could try that. One crude method is to buffer all the polygon features by a small positive number then buffer again by the same small negative number which will join the polygons but it will round off inner corners. It will also introduce a lot of vertices which may not be desirable.