topic Re: Counting points inside a polygon in Geoprocessing Questions

Counting points inside a polygon

AdrianWelsh — Tue, 26 Jan 2016 15:32:37 GMT

This is a fairly "simple" GIS operation but I wanted to ask, is Spatial Join the only, or best, method to calculate this? As described in this article:

30779 - Count the number of point features within a polygon

What I am basically wondering is how to have a continually updated polygon feature that would keep a count of points within it. Does that make sense?

Thanks!

Re: Counting points inside a polygon

AdrianWelsh — Tue, 26 Jan 2016 15:33:18 GMT

...and I know there are issues when points fall outside of the polygon. I found this article that discusses using the Proximity tool to calculate that:

More adventures in overlay: point in polygon | ArcGIS Blog

Re: Counting points inside a polygon

VinceAngelo — Tue, 26 Jan 2016 16:43:29 GMT

You'd need to re-run the operation for each changed geometry, when it is changed. This sort of thing is better left to a database trigger, but then you'd need to be using an enterprise geodatabase.

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Re: Counting points inside a polygon

WendellThompson — Tue, 26 Jan 2016 16:46:52 GMT

Have you tried using the PointCollection object? I'm not sure what platform you're on, but on the ArcGIS Runtime for .NET there is a PointCollection class in this namespace "Esri.ArcGISRuntime.Geometry".

You could use this to build a collection of points, and then transpose them to a polygon as needed. Keeping track of the MapPoint count should be straightforward at this point.

Re: Counting points inside a polygon

forestknutsen1 — Tue, 26 Jan 2016 17:29:36 GMT

You could script the solution with python and then use Windows Task Scheduler to have the operation run every night or more often if needed (every hour, every 30 minutes, or whatever is appropriate for your situation). If python is not your thing one could make it in model builder and the export it to python.

Re: Counting points inside a polygon

AdrianWelsh — Tue, 26 Jan 2016 17:36:28 GMT

This sounds like something that would still have to replace the feature class with, right? Not something that would be an automatic update?

Re: Counting points inside a polygon

AdrianWelsh — Tue, 26 Jan 2016 17:38:24 GMT

I was afraid that I would need to re-run it each time. Would a database trigger be something you would script up in Python or so? And do you have to use an enterprise geodatabase for it?

Re: Counting points inside a polygon

AdrianWelsh — Tue, 26 Jan 2016 17:39:04 GMT

Yeah, this might be something that I might have to do, unfortunately. But, it's still sort of a solution...

Re: Counting points inside a polygon

WendellThompson — Tue, 26 Jan 2016 17:41:47 GMT

As I mentioned, i'm not sure what platform you're working on, but an implementation (in .NET) that comes to mind would be a wrapper class that held a PointCollection as well a Polygon Feature. As the PointCollection was updated, the Polygon would be re-drawn on a graphics layer.

Re: Counting points inside a polygon

VinceAngelo — Tue, 26 Jan 2016 17:46:06 GMT

No, database triggers are generally written in SQL (for which this is a relatively simple operation).

Re: Counting points inside a polygon

VinceAngelo — Tue, 26 Jan 2016 17:52:59 GMT

If the geometry is being continually updated, then the time to make the PCOUNT edit is when the shape is updated (together, in one transaction). Updating the counts in batch would only make sense if all the polygons are edited at the same time, in which case you should make all the edits to an intermediate copy, then update the master after the long-running job is complete.

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Re: Counting points inside a polygon

AdrianWelsh — Tue, 26 Jan 2016 17:53:11 GMT

I'm running ArcGIS 10.3.1 Desktop (ArcMap) on Windows 10, 64-bit. I am not sure that I would want a graphics layer as opposed to a feature class within a geodatabase. And, I am not as familiar with .NET as I once was year ago...

Re: Counting points inside a polygon

AdrianWelsh — Tue, 26 Jan 2016 17:54:42 GMT

Ah, that makes sense.

Re: Counting points inside a polygon

DarrenWiens2 — Tue, 26 Jan 2016 17:54:45 GMT

You could look into creating a Python Add-in Application Extension. See a list of available triggers here. It depends how often you want to run your script, but I expect you would probably want something that triggers fairly regularly, like: onEditorSelectionChanged() or onCurrentTaskChanged() or onSaveEdits(). Your script could be as simple as one line within the add-in event method calling Spatial Join.

Re: Counting points inside a polygon

JimmyKroon — Tue, 26 Jan 2016 18:17:19 GMT

I have a simple python script that will count points within polygons and add the count to a field in the polygon feature class. It's pretty simple and you could run it automatically using a batch file and windows scheduler - or just run the script as needed from explorer. If that sounds helpful I'll find and post it.

Re: Counting points inside a polygon

AdrianWelsh — Tue, 26 Jan 2016 19:41:03 GMT

Thanks Darren, I'll look into that.

Re: Counting points inside a polygon

AdrianWelsh — Tue, 26 Jan 2016 19:41:21 GMT

Jimmy, that sounds awesome. I would love to see it.

Re: Counting points inside a polygon

JimmyKroon — Tue, 26 Jan 2016 19:51:09 GMT

It is attached. You'll need to edit these variables to make it work and the polygon feature class needs an integer field to store the results.

Points = "D:\\Data\\Geodatabase.gdb\\PointFC"
Zones = "D:\\Data\\Geodatabase.gdb\\PolygonFC"

zoneNameField = "NAME"
zoneIncidentsField = "INCIDENTS"

Once your paths and field names are stored you can double-click from windows explorer to run anytime you want.

Re: Counting points inside a polygon

AdrianWelsh — Wed, 27 Jan 2016 21:37:54 GMT

Wow thanks! Great script. Those does exactly what I needed it to do. One question though, what is the point of the "zoneNameField" in this? Doesn't the script just cycle through all of the features within that feature class? If some features had the same zone name, would those get counted the same?

Thanks again.

Re: Counting points inside a polygon

JimmyKroon — Sat, 11 Dec 2021 13:11:13 GMT

zoneNameField is used to build a query which is required to create a feature layer containing one polygon. You could use the objectID field for this value too.

queryString = '"' + zoneNameField + '" = ' + "'" + zoneName + "'"
arcpy.MakeFeatureLayer_management(Zones, "CurrentZoneLayer", queryString)

And yes, if you had multiple polygons with the same name, they would get grouped together for the counts because the query would select them all.