topic Re: Divide Irregular Polygon into 730 parts in Data Management Questions

Divide Irregular Polygon into 730 parts

TysonBarlow — Tue, 06 May 2014 13:25:50 GMT

Hi guys and gals!

Is there a utility or something that I could use to divide an irregularly shaped polygon into 730 pieces, preferably of equal area? For example, take any given state polygon in the US and divide it into 730 pieces.

Thank you!!

Re: Divide Irregular Polygon into 730 parts

JoshuaChisholm — Tue, 06 May 2014 14:21:31 GMT

Hello Tyson,

How do you want to split the polygon? By a road network? Do you want the polygon split into little squares, long slivers or something else?

Let me know, and we might be able to figure something out.

Re: Divide Irregular Polygon into 730 parts

TysonBarlow — Tue, 06 May 2014 14:30:35 GMT

I would like to split it into squares. Being an irregularly shaped polygon, I understand that not all of the 730 squares would be equal area, which is fine. I'd appreciate any help you can give! Something like the screenshot below, but with 730 pieces.
[ATTACH=CONFIG]33624[/ATTACH]

Re: Divide Irregular Polygon into 730 parts

Zeke — Tue, 06 May 2014 15:31:25 GMT

Not sure this will work, but look into Create Fishnet. This can create lines that you could use to split the polygon. Part I'm not sure of is how to guarantee 730 cells. You might be able to divide the area of the polygon by 730 to get cell height & width, but if the fishnet is created on the extent of the polygon rather than the feature itself this might not work.

Re: Divide Irregular Polygon into 730 parts

TysonBarlow — Tue, 06 May 2014 15:34:07 GMT

Yeah, I've tried the fishnet function, and run into the problem you outline here. It creates features on the extent of the polygon and not the feature itself, so I'm having a hard time getting exactly 730 pieces. Thanks for the thought though!

Re: Divide Irregular Polygon into 730 parts

JoshuaChisholm — Tue, 06 May 2014 19:20:58 GMT

Hello Tyson,

I think this might work (sorry if the code is a little messy):

import arcpy arcpy.env.overwriteOutput = True  #set number of desired cells: x=730  #set feature classes: inFC=r'C:\Path\To\Poly.shp' tempGrid=r'C:\Path\To\tempGrid.shp' #just a temporary file outFC=r'C:\Path\To\grid.shp' #final grid  #set default grid variables: extent = arcpy.Describe(inFC).extent origin_coord=str(extent.XMin)+" "+str(extent.YMin) oppositeCoorner=str(extent.XMax)+" "+str(extent.YMax) y_axis_coord=str(extent.XMin)+" "+str(extent.YMin+10) number_rows=number_columns=0 geometryType = 'POLYGON'  #set starting cellSize and increment: cellSize=max(float(extent.width),float(extent.height)) inc=cellSize  countOutFC=0.0 #needed to start while loop  #Find an appropriate cell size: while countOutFC!=x:     if cellSize==inc:         inc=inc/2.0         continue     cell_width=cell_height=cellSize     arcpy.CreateFishnet_management(tempGrid,origin_coord,y_axis_coord,cell_width,cell_height,number_rows,number_columns,oppositeCoorner,"LABELS","#",geometryType)      arcpy.MakeFeatureLayer_management(tempGrid, "temp_lyr")     arcpy.SelectLayerByLocation_management("temp_lyr", "INTERSECT", inFC)      countOutFC=float(arcpy.GetCount_management("temp_lyr").getOutput(0))          print "Cell size: "+str(cellSize)+"  Count: "+str(countOutFC)     if countOutFC>x:         print "Overshot..."         cellSize=prevCellSize         inc=inc/2.0     else:         prevCellSize=cellSize         cellSize-=inc  cellSize=prevCellSize print '\nFound an appropriate cell size: '+str(cellSize)  #Find a simplified cell size: print "\nTrying to simplify..." for i in range(len(str(cellSize))):     simpCellSize=round(cellSize,i)     if simpCellSize==0:         continue     cell_width=cell_height=simpCellSize     arcpy.CreateFishnet_management(tempGrid,origin_coord,y_axis_coord,cell_width,cell_height,number_rows,number_columns,oppositeCoorner,"LABELS","#",geometryType)     arcpy.MakeFeatureLayer_management(tempGrid, "temp_lyr")     arcpy.SelectLayerByLocation_management("temp_lyr", "INTERSECT", inFC)      countOutFC=float(arcpy.GetCount_management("temp_lyr").getOutput(0))     print "Cell size: "+str(simpCellSize)+"  Count: "+str(countOutFC)     if countOutFC==x:         break  if simpCellSize==cellSize:     print "Could not easily find a simplified cell size."     #rerun for last good cellsize (not simplified):     cell_width=cell_height=cellSize     arcpy.CreateFishnet_management(tempGrid,origin_coord,y_axis_coord,cell_width,cell_height,number_rows,number_columns,oppositeCoorner,"LABELS","#",geometryType)     arcpy.MakeFeatureLayer_management(tempGrid, "temp_lyr")     arcpy.SelectLayerByLocation_management("temp_lyr", "INTERSECT", inFC) else:     print "A simplified cell size: "+str(simpCellSize)  arcpy.Select_analysis("temp_lyr",outFC)  print "Done!!!"

The code is a little slow (it took 35 seconds on my fast machine). Let me know how it goes!

Re: Divide Irregular Polygon into 730 parts

TysonBarlow — Tue, 06 May 2014 19:33:51 GMT

Joshua, it worked beautifully! Thank you so much for your help!!

Re: Divide Irregular Polygon into 730 parts

JackDavis — Thu, 10 Jul 2014 17:53:56 GMT

Hi Joshua,

Do you think it would be possible to modify your script to operate on individual polygons inside of a map instead of the map extents? I'm struggling a bit trying to figure out how to divide a map of many ~ 1 mi sections into 100 ~.1 mi sub-sections with labels in each.

Thanks,

Jack

Re: Divide Irregular Polygon into 730 parts

JoshuaChisholm — Fri, 11 Jul 2014 16:33:47 GMT

Hello Jack,

I think this should work (but I didn't have a chance to test).

Let me know how it does. Good luck!

import arcpy  
arcpy.env.overwriteOutput = True  


targetLayers=['farm fields','Municipalities'] #specify all the layers you want (they must have unique names)
mxdpath=r'C:\Path\To\MapDoc.mxd' #point to your mxd


mxd=arcpy.mapping.MapDocument("CURRENT")
lyrs=arcpy.mapping.ListLayers(mxd)
dfName='Layers' #name of the data frame you want to add the new grids to


for lyr in lyrs:
  if not lyr.name in targetLayers:
    continue #Skip all non-target layers
  #set number of desired cells:  
  x=730  
   
  #set feature classes:  
  inFC=lyr 
  tempGrid=r'C:\Path\To\tempGrid.shp' #just a temporary file  
  outFC=r'C:\Path\To\grid_'+lyr.name+'.shp' #final grid 
  
  #delete tempGrid if exists:
  if arcpy.Exists(tempGrid):
    arcpy.Delete_management(tempGrid)

   
  #set default grid variables:  
  extent = arcpy.Describe(inFC).extent  
  origin_coord=str(extent.XMin)+" "+str(extent.YMin)  
  oppositeCoorner=str(extent.XMax)+" "+str(extent.YMax)  
  y_axis_coord=str(extent.XMin)+" "+str(extent.YMin+10)  
  number_rows=number_columns=0  
  geometryType = 'POLYGON'  
   
  #set starting cellSize and increment:  
  cellSize=max(float(extent.width),float(extent.height))  
  inc=cellSize  
   
  countOutFC=0.0 #needed to start while loop  
   
  #Find an appropriate cell size:  
  while countOutFC!=x:  
    if cellSize==inc:  
      inc=inc/2.0  
      continue  
    cell_width=cell_height=cellSize  
    arcpy.CreateFishnet_management(tempGrid,origin_coord,y_axis_coord,cell_width,cell_height,number_rows,number_columns,oppositeCoorner,"LABELS","#",geometryType)  
   
    arcpy.MakeFeatureLayer_management(tempGrid, "temp_lyr")  
    arcpy.SelectLayerByLocation_management("temp_lyr", "INTERSECT", inFC)  
   
    countOutFC=float(arcpy.GetCount_management("temp_lyr").getOutput(0))  
   
    print "Cell size: "+str(cellSize)+"  Count: "+str(countOutFC)  
    if countOutFC>x:  
      print "Overshot..."  
      cellSize=prevCellSize  
      inc=inc/2.0  
    else:  
      prevCellSize=cellSize  
      cellSize-=inc  
   
  cellSize=prevCellSize  
  print '\nFound an appropriate cell size: '+str(cellSize)  
   
  #Find a simplified cell size:  
  print "\nTrying to simplify..."  
  for i in range(len(str(cellSize))):  
    simpCellSize=round(cellSize,i)  
    if simpCellSize==0:  
      continue  
    cell_width=cell_height=simpCellSize  
    arcpy.CreateFishnet_management(tempGrid,origin_coord,y_axis_coord,cell_width,cell_height,number_rows,number_columns,oppositeCoorner,"LABELS","#",geometryType)  
    arcpy.MakeFeatureLayer_management(tempGrid, "temp_lyr")  
    arcpy.SelectLayerByLocation_management("temp_lyr", "INTERSECT", inFC)  
   
    countOutFC=float(arcpy.GetCount_management("temp_lyr").getOutput(0))  
    print "Cell size: "+str(simpCellSize)+"  Count: "+str(countOutFC)  
    if countOutFC==x:  
      break  
   
  if simpCellSize==cellSize:  
    print "Could not easily find a simplified cell size."  
    #rerun for last good cellsize (not simplified):  
    cell_width=cell_height=cellSize  
    arcpy.CreateFishnet_management(tempGrid,origin_coord,y_axis_coord,cell_width,cell_height,number_rows,number_columns,oppositeCoorner,"LABELS","#",geometryType)  
    arcpy.MakeFeatureLayer_management(tempGrid, "temp_lyr")  
    arcpy.SelectLayerByLocation_management("temp_lyr", "INTERSECT", inFC)  
    else:  
      print "A simplified cell size: "+str(simpCellSize)  
   
    arcpy.Select_analysis("temp_lyr",outFC)
    #add new data to mxd
    df = arcpy.mapping.ListDataFrames(mxd, dfName)[0]
    newlayer = arcpy.mapping.Layer(outFC)  
    arcpy.mapping.AddLayer(df, newlayer, "AUTO_ARRANGE")
  
print "Done!!!"

Edit (July 14, 2014): Added lines 25-27

Re: Divide Irregular Polygon into 730 parts

JackDavis — Sun, 13 Jul 2014 14:37:58 GMT

Thanks for the reply Joshua! I didn't have much time to try this out Friday before I left the office, but on initial run, I got an error on the AddLayer call on line 94. The second argument 'addLayer' was undefined. I'll read through it again Monday morning and see if I can figure it out...I may have left something out.

Thanks again,

Jack

Re: Divide Irregular Polygon into 730 parts

JoshuaChisholm — Mon, 14 Jul 2014 14:33:40 GMT

Hello Jack,

I had made an edit to my code shortly after posting. You must have grabbed the wrong code. Line 94 should read: arcpy.mapping.AddLayer(df, newlayer, "AUTO_ARRANGE")

Let me know if that works for you!

Re: Divide Irregular Polygon into 730 parts

JackDavis — Mon, 14 Jul 2014 14:50:03 GMT

Yeah, I noticed this morning that my code didn't match what was here, so I updated it. When I ran the script, I got 100 grids, but it was 100 over the entire map instead of each polygon. Not sure if I set something up wrong or what? Thanks again for the help!

Re: Divide Irregular Polygon into 730 parts

JoshuaChisholm — Mon, 14 Jul 2014 15:32:18 GMT

I think it might be because I was not clearing the "tempGrid" in between iterations. Try adding these line after specifying the location of the "tempGrid" (line 25):

  #delete tempGrid if exists: 
  if arcpy.Exists(tempGrid): 
    arcpy.Delete_management(tempGrid)

I've also edited my post above to reflect these changes.

Re: Divide Irregular Polygon into 730 parts

JackDavis — Mon, 14 Jul 2014 18:51:27 GMT

Well Joshua, it's still just dividing up the entire map layer into 100 grids instead of each polygon in the layer. Not sure if I am doing something wrong on the setup...In looking at the code, is each polygon supposed to be in it's own layer?

Re: Divide Irregular Polygon into 730 parts

JoshuaChisholm — Mon, 14 Jul 2014 19:44:37 GMT

Ohhh, I think I completely misunderstood you. I thought you made multiple layers (pointing to multiple shapefiles/FCs) in an MXD that you wanted to split into a given number of grids. It sounds like you actually want to take a single layer in an MXD and split it into multiple grids. Is this correct?

Do they have to be split into a specific number of grids or into a grids of a specific dimension?

Re: Divide Irregular Polygon into 730 parts

JackDavis — Mon, 14 Jul 2014 19:58:26 GMT

Sorry...I was afraid of that after I started looking closer at the code...Here is a sample of what I'm talking about. It is 1 layer with many polygons in a grid. I need to split each polygon into 100 sub-grids with number labels from 1-100. When I saw your original post, I liked the way the grids were laid out over the layer extents and thought it might work for my situation.

Re: Divide Irregular Polygon into 730 parts

JoshuaChisholm — Tue, 15 Jul 2014 18:22:50 GMT

Hello Jack,

Thank you for the explanation and the picture. I think I now have a much better understanding of your needs. I've created another version of the script. Unfortunately I'm a little short on time and don't have time to test it. If you could let me know what errors pop up, we can fix the script as needed.

import arcpy    
arcpy.env.overwriteOutput = True    
  
#set feature classes:  
inFC=r'C:\Path\To\Poly.shp'  
tempGrid=r'C:\Path\To\tempGrid.shp' #just a temporary file  
outFC=r'C:\Path\To\grid.shp' #final grid 

#set number of desired cells:    
x=100


#set ID field in the input feature class:
idField="ParentID" #set to a field you can use to identify with original record each grid was part of *MUST BE UNIQUE


#get shape field
shapeName = arcpy.Describe(inFC).shapeFieldName


#delete tempGrid if exists:  
if arcpy.Exists(tempGrid):  
  arcpy.Delete_management(tempGrid)  
#delete outFC if exists:  
if arcpy.Exists(outFC):  
  arcpy.Delete_management(outFC)  


#Create output FC (the where statement will select 0 records
arcpy.Select_analysis(inFC, outFC, '"'+idField+'" <> "'+idField+'"') #change double quotes "" to [] if using geodatabases


rows=arcpy.da.SearchCursor(idField,shapeName)
for row in rows:
  where='"'+idField+'" = \''+row.getValue(idField)+'\'' #change double quotes "" to [] if using geodatabases
  #Use this line if your idField is a number: where='"'+idField+'" = '+str(row.getValue(idField)) #change double quotes "" to [] if using geodatabases
  arcpy.MakeFeatureLayer_management(inFC, "master_lyr",where) 
  feat = row.getValue(shapeName)
  
  #set default grid variables:    
  extent = feat.extent   
  origin_coord=str(extent.XMin)+" "+str(extent.YMin)    
  oppositeCoorner=str(extent.XMax)+" "+str(extent.YMax)    
  y_axis_coord=str(extent.XMin)+" "+str(extent.YMin+10)    
  number_rows=number_columns=0    
  geometryType = 'POLYGON'    
     
  #set starting cellSize and increment:    
  cellSize=max(float(extent.width),float(extent.height))    
  inc=cellSize    
     
  countOutFC=0.0 #needed to start while loop    
     
  #Find an appropriate cell size:    
  while countOutFC!=x:    
    if cellSize==inc:    
      inc=inc/2.0    
      continue    
    cell_width=cell_height=cellSize    
    arcpy.CreateFishnet_management(tempGrid,origin_coord,y_axis_coord,cell_width,cell_height,number_rows,number_columns,oppositeCoorner,"LABELS","#",geometryType)    
     
    arcpy.MakeFeatureLayer_management(tempGrid, "temp_lyr")    
    arcpy.SelectLayerByLocation_management("temp_lyr", "INTERSECT", "master_lyr")    
     
    countOutFC=float(arcpy.GetCount_management("temp_lyr").getOutput(0))    
     
    print "Cell size: "+str(cellSize)+"  Count: "+str(countOutFC)    
    if countOutFC>x:    
      print "Overshot..."    
      cellSize=prevCellSize    
      inc=inc/2.0    
    else:    
      prevCellSize=cellSize    
      cellSize-=inc    
     
  cellSize=prevCellSize    
  print '\nFound an appropriate cell size: '+str(cellSize)    
     
  #Find a simplified cell size:    
  print "\nTrying to simplify..."    
  for i in range(len(str(cellSize))):    
    simpCellSize=round(cellSize,i)    
    if simpCellSize==0:    
      continue    
    cell_width=cell_height=simpCellSize    
    arcpy.CreateFishnet_management(tempGrid,origin_coord,y_axis_coord,cell_width,cell_height,number_rows,number_columns,oppositeCoorner,"LABELS","#",geometryType)    
    arcpy.MakeFeatureLayer_management(tempGrid, "temp_lyr")    
    arcpy.SelectLayerByLocation_management("temp_lyr", "INTERSECT", "master_lyr")    
     
    countOutFC=float(arcpy.GetCount_management("temp_lyr").getOutput(0))    
    print "Cell size: "+str(simpCellSize)+"  Count: "+str(countOutFC)    
    if countOutFC==x:    
      break    
     
  if simpCellSize==cellSize:    
    print "Could not easily find a simplified cell size."    
    #rerun for last good cellsize (not simplified):    
    cell_width=cell_height=cellSize    
    arcpy.CreateFishnet_management(tempGrid,origin_coord,y_axis_coord,cell_width,cell_height,number_rows,number_columns,oppositeCoorner,"LABELS","#",geometryType)    
    arcpy.MakeFeatureLayer_management(tempGrid, "temp_lyr")    
    arcpy.SelectLayerByLocation_management("temp_lyr", "INTERSECT", "master_lyr")    
  else:    
    print "A simplified cell size: "+str(simpCellSize)    
     
  arcpy.Append_management("master_lyr",outFC)


del rows
print "Done!!!"

Re: Divide Irregular Polygon into 730 parts

ClaytonHayes — Thu, 18 Jun 2015 16:50:57 GMT

Hi Joshua, I am trying to use your script and I keep getting a runtime error on line 30. Also, I am new to python, what parts of the code do I need to change in order to so it works with my feature class.

Re: Divide Irregular Polygon into 730 parts

Zeke — Wed, 24 Jun 2015 16:34:36 GMT

I don't know if all the quote marks on that line line up properly, but the final character should be ), not <.