I have a shp file in Arcmap 10 that has ~16600 polygons. Some overlap. I want any polygons that are overlapping to be dissolved into single polygons. I want non-overlapping polygons to remain the same. When I use Dissolve as suggested here How to dissolve overlapping polygons? I get about 93000 polygons. Why is it touching my non-overlapping polygons? Only thing I can guess is that it's something to do with polygons that were multipart polygons to begin with and now I've unchecked "create multipart polygons." If that's it, how can I work around that? If not, what gives?
If you mean to keep the attributes meaningful, it makes no sense to dissolve the overlapping polygons if you care about those attributes. Since it appears that dissolve has already occurred, then if your problem is sliver polygons, you should perform an Intersect on the one feature class and then select every polygon in the original that overlaps a small negative buffer on the Intersected features followed by use of the Integrate tool on the original (make a backup first).
If the overlap is more than slivers, show us a picture of these overlaps and explain what attributes you want over those you don't. On the other hand, if you were willing to sacrifice all attributes as suggested in the post you were following, who cares if it is one huge multi-part polygon in the end. All parts of the shape mean the same thing as any other part once you sacrifice the attributes.
If on the other hand you in reality want some attributes to dominate over others, that is a different story, and you then should not let touching polygons that don't overlap be combined in a Dissolve if they have distinct attributes (which the original method you were following would destroy).
If you don't mind a few extra geoprocessing steps, I would suggest a workaround. Before dissolving, perform the following steps. Select all features in your shapefile. This is easy to do with the 'switch selection' button in the shapefile's attribute table. Then perform a select by location, with the shapefile as both the input and the selection feature. For 'selection method', choose
select from the currently selected features in. For spatial selection method, choose
are crossed by the outline of the source layer feature. Perform your selection and overlapping features in your shapefile will be selected. Now you can perform your
dissolve on your shapefile, and the tool will only geoprocess what is selected. Finally, switch your selection on your original shapefile, and
merge it with your dissolve output.
If it's not an ArcGIS bug and you do instead have multipart polygons that you do not want, first use the
multipart to singlepart tool on your shapefile before dissolving.
Use intersect tool with single input, call result OVERLAPS. Select original that intersect OVERLAPS and dissolve originals. Switch selection in originals and merge with dissolved.