topic Re: Count number of features inside polygon in Python Questions

Count number of features inside polygon

CCWeedcontrol — Sun, 12 Dec 2021 05:44:51 GMT

I need some help on my code to count the number of features inside a polygon. I have the following but after testing it, it doesn't seem to be correct. I am trying to figure out how many parcel lots are within the subdivision boundary. My test show after running the code that the "Stats" table has 9 Frequencies but in actually there is 10 parcels within the subdivision. I have tried "HAVE_THEIR_CENTER_IN" but all the results are 1.

import arcpy, os

mxd = arcpy.mapping.MapDocument("current")
df = arcpy.mapping.ListDataFrames(mxd, "Layers")[0]
lyr = arcpy.mapping.ListLayers(mxd, "Taxlots")[0]
subs = arcpy.mapping.ListLayers(mxd, "SubsOutsideCities")[0]
#arcpy.MakeFeatureLayer_management(par, "parLyr")

arcpy.SpatialJoin_analysis(subs, lyr,"in_memory/points_SpatialJoin", "JOIN_ONE_TO_MANY", "KEEP_ALL", "", "CONTAINS")
arcpy.Statistics_analysis("points_SpatialJoin", "in_memory/stats", "Join_Count COUNT","OBJECTID")
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Re: Count number of features inside polygon

DanPatterson_Retired — Thu, 19 Mar 2020 20:41:51 GMT

Your shapes are all singlepart? If not, run the Multipart to singlepart tool

Re: Count number of features inside polygon

CCWeedcontrol — Thu, 19 Mar 2020 20:49:51 GMT

Yes they are all singlepart.

Re: Count number of features inside polygon

DanPatterson_Retired — Thu, 19 Mar 2020 21:02:52 GMT

many to one

one to one

one to many

switch the order of the join

which options did you try?

Re: Count number of features inside polygon

CCWeedcontrol — Thu, 19 Mar 2020 21:08:20 GMT

There is only two options for the spatialJoin_analysis, i am not sure what you mean by the other options.

JOIN_ONE_TO_ONE

JOIN_ONE_TO_MANY

Re: Count number of features inside polygon

JoeBorgione — Thu, 19 Mar 2020 21:15:29 GMT

Looks like you are using ArcMap to perform you analysis. You might try to do it by hand, and then go to the geoprocessing results button; that'll tell what ArcMap just did for you and you can use that in your python coding. I do that all the time with tools in Pro.

Re: Count number of features inside polygon

CCWeedcontrol — Thu, 19 Mar 2020 21:54:59 GMT

I have tried that and get the same results.

Re: Count number of features inside polygon

RandyBurton — Sun, 12 Dec 2021 05:44:54 GMT

Perhaps something like:

countFC = 'polygons'  # feature containing outer polygons
countFld = ['ParcelCount', 'SHAPE@'] # ParcelCount is for count results, SHAPE@ is geometry of polygon

parcels = 'parcels' # parcels to be counted

with arcpy.da.UpdateCursor(countFC, countFld) as cursor: # cycle through outer polygon layer
    for row in cursor:
        arcpy.management.SelectLayerByLocation(parcels, "HAVE_THEIR_CENTER_IN", row[1], "", "NEW_SELECTION") # row[1] is SHAPE@
        row[0] = int(arcpy.GetCount_management(parcels)[0]) # row[0] to be updated with count
        cursor.updateRow(row) # update row‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: Count number of features inside polygon

DanPatterson_Retired — Thu, 19 Mar 2020 22:28:12 GMT

save the result to disk, and open the table showing the OBJECTID for the join count.

click on every feature in turn and see if one of the features is actually 2 parts, or one feature is partially on top of the other

Re: Count number of features inside polygon

CCWeedcontrol — Sun, 12 Dec 2021 05:44:57 GMT

Randy I was able to get to work, thanks for the help.

import arcpy

mxd = arcpy.mapping.MapDocument("current")
df = arcpy.mapping.ListDataFrames(mxd, "Layers")[0]
lyr = arcpy.mapping.ListLayers(mxd, "Taxlots")[0]
subs = arcpy.mapping.ListLayers(mxd, "SubsOutsideCities")[0]
#arcpy.MakeFeatureLayer_management(par, "parLyr")

with arcpy.da.UpdateCursor(subs, ["VxCount1", "Shape@"]) as cursor: # cycle through outer polygon layer
    for row in cursor:
        arcpy.management.SelectLayerByLocation(lyr, "HAVE_THEIR_CENTER_IN", row[1]) # row[1] is SHAPE@
        row[0] = int(arcpy.GetCount_management(lyr)[0]) # row[0] to be updated with count
        cursor.updateRow(row) # update row‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: Count number of features inside polygon

CCWeedcontrol — Sun, 12 Dec 2021 05:45:00 GMT

If i run the following in stand alone python, every value in VxCount1 has the same number.

subs = r'C:\Temp\SubsOutsideCities_Temp.shp'
lyr = r'C:\Temp\TaxParcels.shp'

with arcpy.da.UpdateCursor(subs, ["VxCount1", "Shape@"]) as cursor: # cycle through outer polygon layer
    for row in cursor:
        arcpy.management.SelectLayerByLocation(lyr, "HAVE_THEIR_CENTER_IN", row[1]) # row[1] is SHAPE@
        row[0] = int(arcpy.GetCount_management(lyr)[0]) # row[0] to be updated with count‍‍‍‍‍‍‍
        cursor.updateRow(row) # update row‍‍‍‍‍‍‍‍

Re: Count number of features inside polygon

RandyBurton — Fri, 20 Mar 2020 19:30:25 GMT

You may need to use Make Feature Layer to convert your shape file into a "layer".

Re: Count number of features inside polygon

CCWeedcontrol — Sun, 12 Dec 2021 05:45:03 GMT

Got it to work with making a feature layer. and adding row 10

lyr = r'C:\Temp\TaxParcels.shp'
subs = r'C:\Temp\SubsOutsideCities_Temp.shp'
arcpy.MakeFeatureLayer_management(lyr, "parLyr")


with arcpy.da.UpdateCursor(subs, ["VxCount", "Shape@"]) as cursor: # cycle through outer polygon layer
    for row in cursor:
        arcpy.management.SelectLayerByLocation("parLyr", "HAVE_THEIR_CENTER_IN",row[1]) # row[1] is SHAPE@
        count = int(arcpy.GetCount_management("parLyr")[0])# row[0] to be updated with count
        row[0] = (count)
        cursor.updateRow(row) # update row‍‍‍‍‍‍‍‍‍‍‍