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I have a GeoJSON FeatureCollection object made up of several polygons and I would like to select the markers which lie within each polygon. The information contained within the markers is to be used to show average stats for each polygon.

I have seen some suggesting using http://turfjs.org/docs/#within or http://turfjs.org/docs/#inside.

Markers are simply in L.Marker form. I intend to use the onEachFeature function to have a popup for each polygon. Has anyone done this before and can recommend the best method?

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2

I've done something similar, I used the draw tool to create a polygon and select the points inside. Your task is a little different. I did use the TURF JS CDN in my HTML head.

I read my GeoJSON in to a layer called allPoints, I had points and used icon instead of markers but same concept. My code below shows layer.toGeoJSON basically this is the Leaflet polygon. I would modify it to loop through the polygons and the turf.within will capture the points.

var shape2 = allPoints.toGeoJSON()

var ptsWithin2 = turf.within(shape2, layer.toGeoJSON());

alert('Found ' + ptsWithin2.features.length + ' features');
alert("results "+JSON.stringify(ptsWithin2));

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  • Thanks. I've done var searchWithin = { "type": "FeatureCollection", "features": [ { "type": "Feature", "properties": {}, "geometry": { "type": "Polygon", "coordinates": [[]]}}]}; using just one polygon and the coordinates for it. My markers aren't GeoJSON they are just L.Markers, would your method still work? Thanks – sm29 May 2 '17 at 21:29
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    I think I used .toGeoJSON() to convert it for turf, looks like markers should work in the same way. leafletjs.com/reference.html#marker-togeojson – Bill Chappell May 2 '17 at 21:43
  • Thanks, I have it set up like this gist.github.com/mattspencer29/c233623f12c3d913c23eb9ef3b8dddd9. I would just like it to return each marker in each polygon (using GeoJSON properties or coordinates). – sm29 May 3 '17 at 9:22
  • I've been able to draw your polygons, I made a simple point layer and can symbolize it based on ratings. Your gist has two polygon layers and refers to to a PHP file (not included) for the points. How do you see this working? Do you select a single polygon and it selects points inside it? Do you export the selected points out or somehow highlight them? I'm confused here as to what your end game is. – Bill Chappell May 3 '17 at 15:16
  • Thanks. I basically want to find the mean hygieneData[i].rating_value for each polygon. Each marker contains a rating value and therefore i need to export or have a method which returns each marker so i can find the mean. – sm29 May 3 '17 at 20:35
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Here is an example of the logic working. My test point are already GeoJSON, I have PHP echo these as GeoJSON. Copy/Paste this HTML example to see it run the Modify as needed.

     <html>
<head>
  <meta charset=utf-8 />
  <title>Points Within</title>
  <meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />

  <!-- Load Leaflet from CDN-->
  <link rel="stylesheet" href="https://unpkg.com/leaflet@1.0.3/dist/leaflet.css" />
  <script src="https://unpkg.com/leaflet@1.0.3/dist/leaflet-src.js"></script>

    <script src="https://npmcdn.com/@turf/turf/turf.min.js"></script>
  <style>
    body { margin:0; padding:0; }
    #map { position: absolute; top:0; bottom:0; right:0; left:0; }
  </style>
</head>
<body>
<div id="map"></div>
<script>

var searchWithin = {
"type": "FeatureCollection",
"features": [
{ "type": "Feature", "properties": { "Id": 0, "Zone": 1 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ -1.576983165430079, 53.917874213202538 ], [ -1.575668840812682, 53.833757437687211 ], [ -1.662610537969044, 53.833939896652851 ], [ -1.662434014051257, 53.918053543420058 ], [ -1.576983165430079, 53.917874213202538 ] ] ] } },
{ "type": "Feature", "properties": { "Id": 0, "Zone": 2 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ -1.575668840812682, 53.833757437687211 ], [ -1.576983165430079, 53.917874213202538 ], [ -1.48383238441653, 53.917678723630672 ], [ -1.484008908334317, 53.833565076863636 ], [ -1.575668840812682, 53.833757437687211 ] ] ] } }
]}
//////////////////
var dataPts = {
"type": "FeatureCollection",
"features": [
{ "type": "Feature", "properties": { "ID": 1, "Lat": 53.89179593, "Lng": -1.62117004, "Rating": 1 }, "geometry": { "type": "Point", "coordinates": [ -1.62117004, 53.89179593 ] } },
{ "type": "Feature", "properties": { "ID": 2, "Lat": 53.8747, "Lng": -1.6239166, "Rating": 3 }, "geometry": { "type": "Point", "coordinates": [ -1.6239166, 53.8747 ] } },
{ "type": "Feature", "properties": { "ID": 3, "Lat": 53.88086, "Lng": -1.556625, "Rating": 2 }, "geometry": { "type": "Point", "coordinates": [ -1.556625, 53.88086 ] } },
{ "type": "Feature", "properties": { "ID": 4, "Lat": 53.863, "Lng": -1.518173, "Rating": 3 }, "geometry": { "type": "Point", "coordinates": [ -1.518173, 53.863 ] } },
{ "type": "Feature", "properties": { "ID": 5, "Lat": 53.8707, "Lng": -1.607437133, "Rating": 1 }, "geometry": { "type": "Point", "coordinates": [ -1.607437133, 53.8707 ] } }
]}
////////////////
    var map = L.map('map').setView([53.88, -1.5], 11);

    //basemap
    var osm=new L.tileLayer('http://{s}.tile.osm.org/{z}/{x}/{y}.png',{ 
                attribution: '&copy; <a href="http://osm.org/copyright">OpenStreetMap</a> contributors'});
    osm.addTo(map);

    var polyList = {};

    var myPolyLayer = L.geoJSON();
    myPolyLayer.addData(searchWithin);

    var geojsonMarkerOptions = {
    radius: 8,
    fillColor: "#ff7800",
    color: "#000",
    weight: 1,
    opacity: 1,
    fillOpacity: 0.8
    };

    var myPts = L.geoJSON(null, {
        pointToLayer: function (feature, latlng) {
            return L.circleMarker(latlng, geojsonMarkerOptions);
        }
    })

    myPts.addData(dataPts);

//  myPolyLayer.addTo(map);
    myPts.addTo(map);

    myPolyLayer.eachLayer(function(layer) {

      var coords = layer.feature.geometry.coordinates;

        var polygon = turf.polygon(coords);
        var polygon2 =L.geoJson(polygon, {color: 'red'}).addTo(map);            
        var ptsWithin4 = turf.within(myPts.toGeoJSON(), polygon2.toGeoJSON());
        console.log( ptsWithin4.features.length +" points in this poly");
        alert("results "+JSON.stringify(ptsWithin4));

    })

</script>
</body>
</html>
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