topic Count all points in all polygons in a feature layer when map is loaded in ArcGIS JavaScript Maps SDK Questions

Count all points in all polygons in a feature layer when map is loaded

ChristianDebono — Mon, 21 Apr 2014 07:41:49 GMT

I have two layers. One containing points and the other containing polygons.

I would like to count the number of points belonging to a polygon when the map loads for all the polygons in the feature layer using ArcGIS Javascript API. I have this functionality but it is affecting the performance of the map, since it is updating when the map is updated.

     var polygonFeature = new FeatureLayer("feature layer with polygons", {             mode: FeatureLayer.MODE_ONDEMAND,             outFields: ["*"]         });     map.on("update-end", function () {                     array.forEach(polygonFeature.graphics, function (feature) {                         var name = feature.attributes.NAME;                         var query = new Query();                         var queryTask = new QueryTask("feature layer with points");                         query.geometry = feature.geometry                         query.returnGeometry = true;                          queryTask.executeForCount(query, function (count) {                             console.log("Locality " + name + " has " + count + " points");                         });                     });                 });

Re: Count all points in all polygons in a feature layer when map is loaded

KenBuja — Sat, 11 Dec 2021 10:55:31 GMT

If you're adding the layers to the map using map.addLayers, then you can use the event "layers-add-result". This event fires after all the layers have been added to the map.

You could also still use the "update-end" event, but have it run only a single time. The dojo/on event handler has the once function, which will remove the event listener after running once.

require(["dojo/on"], function(on){
  on.once(map, "update-end", function(){
    // will only fire once...
  });
});

Re: Count all points in all polygons in a feature layer when map is loaded

ChristianDebono — Mon, 21 Apr 2014 12:14:34 GMT

Thanks for the reply Ken Buja, I have tried the "on.once" it works, but its not letting me zoom on the map

Re: Count all points in all polygons in a feature layer when map is loaded

KenBuja — Mon, 21 Apr 2014 12:26:49 GMT

Can you post your code to see what's going on?

Re: Count all points in all polygons in a feature layer when map is loaded

ChristianDebono — Sat, 11 Dec 2021 10:55:33 GMT

function countReport() {
    require(["dojo/on", "dojo/_base/array", "esri/layers/FeatureLayer", "esri/tasks/query", "esri/tasks/QueryTask", "esri/symbols/SimpleFillSymbol", "esri/symbols/SimpleLineSymbol", "esri/graphic", "dojo/_base/Color"],
    function (on, array, FeatureLayer, Query, QueryTask, SimpleFillSymbol, SimpleLineSymbol, Graphic, Color) {
        var polygonFeature = new FeatureLayer("polygon feature layer", {
            mode: FeatureLayer.MODE_ONDEMAND,
            outFields: ["*"]
        });

        map.addLayer(polygonFeature);

        on.once(map, "update-end", function () {
            array.forEach(polygonFeature.graphics, function (feature) {
                var name = feature.attributes.NAME;
                var query = new Query();
                var queryTask = new QueryTask("points feature layer");
                query.geometry = feature.geometry
                query.returnGeometry = true;

                queryTask.executeForCount(query, function (count) {
                    console.log("Locality " + name + " has " + count + " points");                   
                });
            });
        });

    });
}

Re: Count all points in all polygons in a feature layer when map is loaded

KenBuja — Mon, 21 Apr 2014 13:07:59 GMT

This code works and keeps the ability to zoom in and out. Are there other things going on in your code that are causing errors? For example, when I used your code to get the number of cities in each state, I started running into proxy errors (too many city geometries returned, possibly) and other problems. Do you need the geometry returned if you're only doing a count?

<!DOCTYPE html> <html> <head>     <meta http-equiv="Content-Type" content="text/html; charset=utf-8">     <meta name="viewport" content="initial-scale=1, maximum-scale=1,user-scalable=no" />     <title>Simple Map</title>     <link rel="stylesheet" href="http://js.arcgis.com/3.9/js/esri/css/esri.css">     <style>         html, body, #map {             height: 100%;             width: 100%;             margin: 0;             padding: 0;         }          body {             background-color: #FFF;             overflow: hidden;             font-family: "Trebuchet MS";         }     </style>     <script src="http://js.arcgis.com/3.9/"></script>     <script>         var map;          require(["esri/map", "esri/layers/FeatureLayer", "esri/tasks/query", "esri/tasks/QueryTask", "dojo/on", "dojo/_base/array", "dojo/domReady!"],             function (Map, FeatureLayer, Query, QueryTask, on, array) {                 map = new Map("map", {                     basemap: "topo",                     center: [-122.45, 37.75], // longitude, latitude                     zoom: 7                 });                  var polygonLayer = new FeatureLayer("http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Specialty/ESRI_StatesCitiesRivers_USA/MapServer/2", {                     mode: FeatureLayer.MODE_ONDEMAND,                     outFields: ["*"]                 });                  var pointsLayer = new FeatureLayer("http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Specialty/ESRI_StatesCitiesRivers_USA/MapServer/0", {                     mode: FeatureLayer.MODE_ONDEMAND,                     outFields: ["*"]                 });                  map.addLayers([polygonLayer, pointsLayer]);                  on.once(map, "update-end", function () {                     var query = new Query();                     query.where = "STATE_NAME = 'California'";                     var queryTask = new QueryTask("http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Specialty/ESRI_StatesCitiesRivers_USA/MapServer/0");                     queryTask.executeForCount(query, function (count) {                         console.log("California has " + count + " cities");                     });                      //array.forEach(polygonLayer.graphics, function (feature) {                     //    var name = feature.attributes.STATE_NAME;                     //    var query = new Query();                     //    var queryTask = new QueryTask("http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Specialty/ESRI_StatesCitiesRivers_USA/MapServer/0");                     //    query.geometry = feature.geometry                     //    query.returnGeometry = true;                      //    queryTask.executeForCount(query, function (count) {                     //        console.log("Locality " + name + " has " + count + " points");                     //    });                     //});                 });              });     </script> </head>  <body>     <div id="map"></div> </body> </html>