how to make clusters from small polygons with constraint of boundary touching?

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03-11-2015 12:06 PM
waqarahmad
New Contributor III

I want to make some clusters from a bunch of small polygons with the constraint that each basic unit (polygon) in the resultant cluster must share a portion of its boundary with at least one other basic unit (polygon) in the same cluster. This is becuase of the reason that i want the resultant clusters contagious.

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DarrenWiens2
MVP Honored Contributor

You can pull out polygons intersecting at least one other polygon using the following script:

>>> polys = []
... outPolys = []
... with arcpy.da.SearchCursor("YOUR_POLYGON_LAYER_HERE","SHAPE@") as cursor:
...    for row in cursor:
...        polys.append(row[0])
... for i in range(len(polys)):
...    overlap = 0
...    for j in range(len(polys)):
...        if polys.distanceTo(polys) == 0:
...            overlap = overlap + 1
...    if overlap > 1:
...        outPolys.append(polys)       
... arcpy.CopyFeatures_management(outPolys,'in_memory\polys')

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5 Replies
DarrenWiens2
MVP Honored Contributor

How do you want to deal with overlapping polygons (e.g. area of smaller polygon may fully overlap, but boundary may be far inside the larger polygon)?

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waqarahmad
New Contributor III

i have only polygons which touching EACH OTHER'S boundry

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DarrenWiens2
MVP Honored Contributor

You can pull out polygons intersecting at least one other polygon using the following script:

>>> polys = []
... outPolys = []
... with arcpy.da.SearchCursor("YOUR_POLYGON_LAYER_HERE","SHAPE@") as cursor:
...    for row in cursor:
...        polys.append(row[0])
... for i in range(len(polys)):
...    overlap = 0
...    for j in range(len(polys)):
...        if polys.distanceTo(polys) == 0:
...            overlap = overlap + 1
...    if overlap > 1:
...        outPolys.append(polys)       
... arcpy.CopyFeatures_management(outPolys,'in_memory\polys')

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yosukekimura
New Contributor III

I haven't tested, but

     p.disjoint(q)

intead of

     p.distanceTo(q)==0

may runs faster particularly when there are a bunch of polygon.

your method is O(n^2) so may have trouble with large number of polygons...

yosukekimura
New Contributor III

Darren's method should work, and this is an alternative.

# make table of pair of zero distance
arcpy.GenerateNearTable_analysis(fcOrig, fcOrig, tblNear, "0", 
    "NO_LOCATION", "NO_ANGLE", "CLOSEST", "0")

if int(arcpy.GetCount_management(tblNear).getOutput(0)) > 0:
  # grab ids that showed up in the table 
  ids = set([ _[0] for _ in  arcpy.da.SearchCursor(tblNear,('IN_FID'))])

  # grab shape 
  oid = arcpy.Describe(fcOrig).OIDFieldName
  outpoly = [_[0] for _ in arcpy.da.SearchCursor(fcOrig, [ 'SHAPE@, oid]) 
      if _[1] in ids ]

  # save
  arcpy.CopyFeatures_management(outpoly, fcTouching)