Merging polygons that share one vertex (node neighbors) using ArcGIS Desktop?

Question

I have a set of very large shapefiles and would like to merge polygons within these that share one vertex.

Currently they are all separate like so:

What tool can I use to merge all the polygons that share one vertex so in the above example the selected polygon would be part of the one to the left like so:

I would investigate Polygon Neighbors which I believe can recognize polygons that share one vertex (i.e. are node neighbors). — PolyGeo, May 09 '19 at 09:19
Convert back to integer raster, region group, to polygons, dissolve to multipart. — FelixIP, May 09 '19 at 19:51
@FelixIP That worked! Thanks for the help. If you post as an answer I'll accept it. — tom91, May 10 '19 at 10:44

FelixIP · Accepted Answer · 2019-05-12T05:21:23.973

Suggestion in my comments "Convert back to integer raster, region group, to polygons, dissolve to multipart" will work for polygons derived from rasters.

However in general it's better to start with suggestion by @Polygeo . You'll need to use script though:

import arcpy
import networkx as nx
##  replace 2 lines below to point to polygons and neighbours table
Nodes=r'C:\SCRATCH\SCRATCH.gdb\R2P'
Links=r'C:\SCRATCH\SCRATCH.gdb\NBRS'
fldFROM,fldTO="src_OBJECTID","nbr_OBJECTID"
G=nx.Graph()
with arcpy.da.SearchCursor(Links, (fldFROM,fldTO)) as cursor:
    for f,t in cursor:
        G.add_edge(int(f),int(t))
d,N=dict(),1
for group in nx.connected_components(G):
    for n in group:d[n]=N
    N+=1
with arcpy.da.UpdateCursor(Nodes, ("OBJECTID","GRP")) as cursor:
    for k, v in cursor:
        if k in d:v=d[k]
        else: N+=1;v=N
        cursor.updateRow((k,v))

Script assumes that your neighborhood table called NBRS, your polygons stored in file GDB and there is a field called "GRP" to store group numbers.

Thank you, this worked in my instance, but I'll keep that script in mind too! — tom91, May 13 '19 at 08:12

score 0 · Answer 2 · answered May 09 '19 at 08:42

0

If the polygons are really connected to each other, a Union will merge the neighbors.

answered May 09 '19 at 08:42

bugmenot123

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Unfortunately, I've tried Union, including with an xy tolerance but it still produces a shape file where polygons sharing a vertex are separate. They definitely share a vertex because the shape files were made via converting a raster. Is there something else I can try? – tom91 May 09 '19 at 08:52

Merging polygons that share one vertex (node neighbors) using ArcGIS Desktop?

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