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Arcade expression to count points in polygons

CMcDonald

Hi, I want to build an arcade expression that will count the number of points in a polygon layer.

So for example I have a polygon layer called "Data Zones" and a point layer called "Bus Stops". I want to count the number of Bus Stops that are in each Data Zone. Both Layers will be in the same web map.

I believe I have to use the Intersects and Count functions and the expression has to be in the Polygon layer , I just can't can't get an expression to successfully work.

Thanks in advance

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Accepted answers

CMcDonald

I managed to get this expression to work but don't understand how the 'bus' and 'Bus' text works?!

XanderBakker

Hi C McDonald ,

Let me try to provide some explanation on what you have created:

The first line assigns to variable "bus" the featureset (layer) that is accessed using the FeatureSetByName function. This function in your case will find a layer called "Bus Facilities" in your map ($map). In addition you optimize the expression by limiting the fields and not requesting the geometry.
The second line, has two nested functions. The Intersects will intersect the bus facilities featureset stored in variable "bus" obtained on line 1 and intersect it with the current feature (the data zone the user clicked on). This will return all the bus facilities in the current polygon. The Count function will then count the number of bus facilities found in the data zone.
Line 3 returns the number of bus facilities in the data zone determined on line 2.

Later on you might want to extend the expression and list some details of each bus facility found. This is also possible with Arcade.

All comments

CMcDonald

I managed to get this expression to work but don't understand how the 'bus' and 'Bus' text works?!

XanderBakker

Hi C McDonald ,

Let me try to provide some explanation on what you have created:

The first line assigns to variable "bus" the featureset (layer) that is accessed using the FeatureSetByName function. This function in your case will find a layer called "Bus Facilities" in your map ($map). In addition you optimize the expression by limiting the fields and not requesting the geometry.
The second line, has two nested functions. The Intersects will intersect the bus facilities featureset stored in variable "bus" obtained on line 1 and intersect it with the current feature (the data zone the user clicked on). This will return all the bus facilities in the current polygon. The Count function will then count the number of bus facilities found in the data zone.
Line 3 returns the number of bus facilities in the data zone determined on line 2.

Later on you might want to extend the expression and list some details of each bus facility found. This is also possible with Arcade.

CMcDonald

Thanks Xander Bakker, that's helpful. I think I understand a bit more clearly now.

With reference to your last comment I actually have a field in the Bus Facilities Layer called which lists the type. There are 3 types of entries: Bus Stop, Bus Shelter and Unknown.

So in theory I could generate a Count for each of these?

XanderBakker

Hi C McDonald ,

That is indeed something you could do, using the GroupBy function. Have a look at the expression below:

Please note that I am using a name "FacilityType" for the field that contains the facility type, this should be replaced by the actual name of the field. (changes are required on lines 4, 17 and 22)
The script starts the same, accessing the bus facilities on line 4 and reducing the number of field o only the facility type field.
On line 7 the facilities are intersected with the data zone ($feature) and on line 10 a count is done of the facilities
On line 14 the this count is used to define how to proceed. If there are no bus facilities, it will not do the GroupBy and simply return a message "No bus facilities found" (see line 26
When you have bus facilities, the groupby is performed on line 17 with the COUNT statistics type grouping the facility types
On line 20 the first line of the result is generated which will show the total number of bus facilities found in the data zone
The loop on lines 21 to 23 will add a line for each facility type, showing the facility type description and the count
the result is returned on line 29

<SPAN class="comment token">// replace "FacilityType" with the real name of the field!</SPAN>

<SPAN class="comment token">// get the bus layer with only the field that contains the facility type</SPAN>
<SPAN class="keyword token">var</SPAN> bus_fs <SPAN class="operator token">=</SPAN> <SPAN class="token function">FeatureSetByName</SPAN><SPAN class="punctuation token">(</SPAN>$map<SPAN class="punctuation token">,</SPAN> <SPAN class="string token">"Bus Facilities"</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="punctuation token">[</SPAN><SPAN class="string token">"FacilityType"</SPAN><SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">,</SPAN> False<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN>

<SPAN class="comment token">// Intersect the bus featureset with the current data zone ($feature)</SPAN>
<SPAN class="keyword token">var</SPAN> bus_facilities <SPAN class="operator token">=</SPAN> <SPAN class="token function">Intersects</SPAN><SPAN class="punctuation token">(</SPAN>bus_fs<SPAN class="punctuation token">,</SPAN> $feature<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN>

<SPAN class="comment token">// count al bus facilities</SPAN>
<SPAN class="keyword token">var</SPAN> cnt <SPAN class="operator token">=</SPAN> <SPAN class="token function">Count</SPAN><SPAN class="punctuation token">(</SPAN>bus_facilities<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN>

<SPAN class="comment token">// validate if there are bus facilities</SPAN>
<SPAN class="keyword token">var</SPAN> result <SPAN class="operator token">=</SPAN> <SPAN class="string token">""</SPAN><SPAN class="punctuation token">;</SPAN>
<SPAN class="keyword token">if</SPAN> <SPAN class="punctuation token">(</SPAN>cnt <SPAN class="operator token">></SPAN> <SPAN class="number token">0</SPAN><SPAN class="punctuation token">)</SPAN> <SPAN class="punctuation token">{</SPAN>
    <SPAN class="comment token">// there are bus facilities found</SPAN>
    <SPAN class="comment token">// apply groupby to create a count per facility type</SPAN>
    <SPAN class="keyword token">var</SPAN> stats <SPAN class="operator token">=</SPAN> <SPAN class="token function">GroupBy</SPAN><SPAN class="punctuation token">(</SPAN>bus_facilities<SPAN class="punctuation token">,</SPAN> <SPAN class="string token">"FacilityType"</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="punctuation token">[</SPAN><SPAN class="punctuation token">{</SPAN>name<SPAN class="punctuation token">:</SPAN> <SPAN class="string token">"FacilityCount"</SPAN><SPAN class="punctuation token">,</SPAN> expression<SPAN class="punctuation token">:</SPAN> <SPAN class="string token">"FacilityType"</SPAN><SPAN class="punctuation token">,</SPAN> statistic<SPAN class="punctuation token">:</SPAN> <SPAN class="string token">"COUNT"</SPAN> <SPAN class="punctuation token">}</SPAN><SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN>

    <SPAN class="comment token">// loop through the statistics to create the result</SPAN>
    result <SPAN class="operator token">=</SPAN> cnt <SPAN class="operator token">+</SPAN> <SPAN class="string token">" bus facilities found:"</SPAN><SPAN class="punctuation token">;</SPAN>
        <SPAN class="keyword token">for</SPAN> <SPAN class="punctuation token">(</SPAN><SPAN class="keyword token">var</SPAN> stat <SPAN class="keyword token">in</SPAN> stats<SPAN class="punctuation token">)</SPAN> <SPAN class="punctuation token">{</SPAN>
            result <SPAN class="operator token">+</SPAN><SPAN class="operator token">=</SPAN> TextFormatting<SPAN class="punctuation token">.</SPAN>NewLine <SPAN class="operator token">+</SPAN> <SPAN class="string token">" - "</SPAN> <SPAN class="operator token">+</SPAN> stat<SPAN class="punctuation token">.</SPAN>FacilityType <SPAN class="operator token">+</SPAN> <SPAN class="string token">"  ("</SPAN> <SPAN class="operator token">+</SPAN> stat<SPAN class="punctuation token">.</SPAN>FacilityCount <SPAN class="operator token">+</SPAN> <SPAN class="string token">")"</SPAN><SPAN class="punctuation token">;</SPAN>
        <SPAN class="punctuation token">}</SPAN>        
<SPAN class="punctuation token">}</SPAN> <SPAN class="keyword token">else</SPAN> <SPAN class="punctuation token">{</SPAN>
    <SPAN class="comment token">// there are NO bus facilities found</SPAN>
    result <SPAN class="operator token">=</SPAN> <SPAN class="string token">"No bus facilities found"</SPAN><SPAN class="punctuation token">;</SPAN>
<SPAN class="punctuation token">}</SPAN>

<SPAN class="keyword token">return</SPAN> result<SPAN class="punctuation token">;</SPAN>‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍<SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

Not sure if this will work for you, since I don't have the data to test the expression against.

SarahHartholt

Wondering if it is possible to use this expression (or something similar) to display dynamic text in a map layout. I would like to display a count of points within a polygon in the map display. This is what I have so far but keep getting a table not found error:

var Licence = 
 Distinct($feature["xyz.LicenceID"])
var Buff = FeatureSetByName($datastore, "Buffer_of_Site_Address_Points_500m",["BuferDist"], True)
var countSTA = Count(Intersects(Buff,Licence))
return countSTA

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