Query a feature layer (SQL)

Learn how to execute a SQL query to access polygon features in a feature layer.

A feature layer can contain a large number of features stored in ArcGIS. To access a subset of the features, you can execute a SQL or spatial query, or both at the same time. You can also return the attributes, geometry, or both attributes and geometry for each record. SQL and spatial queries are useful when a feature layer is very large and you just want to access a subset of the data.

In this tutorial, you perform server-side SQL queries to return a subset of the features from the LA County Parcel feature layer. The feature layer contains over 2.4 million features. The resulting features are displayed as graphics on the map. A pop-up is also used to display feature attributes.

Prerequisites

Steps

Create a new pen

1. To get started, either complete the Display a map tutorial or use this pen.

Set the API key

To access location services, you need an API key or OAuth 2.0 access token. To learn how to create and scope your key, visit the Create an API key tutorial.

1. Go to your dashboard to get an API key. The API key must be scoped to access the services used in this tutorial.

2. In CodePen, update apiKey to use your key.

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         const map = L.map("map", {
           minZoom: 2
         })
   
         map.setView([34.02, -118.805], 13);
   
         const apiKey = "YOUR_API_KEY";
   
         const basemapEnum = "arcgis/streets";
   
         L.esri.Vector.vectorBasemapLayer(basemapEnum, {
           apiKey: apiKey
         }).addTo(map);
   

Create a SQL selector

ArcGIS feature layers support a standard SQL query where clause. Use a drop-down select element to provide a list of SQL queries for the LA County Parcels feature layer.

1. Create a QueryControl using the L.Control class. Create an on onAdd function that contains each where clause. The selector containing the where clauses will not be removed from the map.

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         L.esri.Vector.vectorBasemapLayer(basemapEnum, {
           apiKey: apiKey
         }).addTo(map);
   
   
   
         L.Control.QueryControl = L.Control.extend({
           onAdd: function (map) {
             const whereClauses = [
               "Choose a WHERE clause...",
               "UseType = 'Residential'",
               "UseType = 'Government'",
               "UseType = 'Irrigated Farm'",
               "TaxRateArea = 10853",
               "TaxRateArea = 10860",
               "TaxRateArea = 08637",
               "Roll_LandValue > 1000000",
               "Roll_LandValue < 1000000"
             ];
   
           },
   
           onRemove: function (map) {
             // Nothing to do here
           }
         });
   

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2. Create a select dropdown to display the whereClauses.

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         L.Control.QueryControl = L.Control.extend({
           onAdd: function (map) {
             const whereClauses = [
               "Choose a WHERE clause...",
               "UseType = 'Residential'",
               "UseType = 'Government'",
               "UseType = 'Irrigated Farm'",
               "TaxRateArea = 10853",
               "TaxRateArea = 10860",
               "TaxRateArea = 08637",
               "Roll_LandValue > 1000000",
               "Roll_LandValue < 1000000"
             ];
   
             const select = L.DomUtil.create("select", "");
             select.setAttribute("id", "whereClauseSelect");
             select.setAttribute("style", "font-size: 16px;padding:4px 8px;");
             whereClauses.forEach(function (whereClause) {
               let option = L.DomUtil.create("option");
               option.innerHTML = whereClause;
               select.appendChild(option);
             });
             return select;
   
           },
   
           onRemove: function (map) {
             // Nothing to do here
           }
         });
   

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3. Add the QueryControl to the map.

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           onRemove: function (map) {
             // Nothing to do here
           }
         });
   
         L.control.queryControl = function (opts) {
           return new L.Control.QueryControl(opts);
         };
   
         L.control
           .queryControl({
             position: "topright"
           })
           .addTo(map);
   

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Add the parcel layer

Use the FeatureLayer class to access the LA County Parcel feature layer. Since you are performing a server-side query, you can hide the features until a SQL query is selected.

1. Create a FeatureLayer and set the url with the LA County Parcel service URL.

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         L.control
           .queryControl({
             position: "topright"
           })
           .addTo(map);
   
         const parcels = L.esri
           .featureLayer({
             url: "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/LA_County_Parcels/FeatureServer/0",
             simplifyFactor: 0.5,
             precision: 4,
   
           })
           .addTo(map);
   

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2. Hide all features in the layer using a layer definition.

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         const parcels = L.esri
           .featureLayer({
             url: "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/LA_County_Parcels/FeatureServer/0",
             simplifyFactor: 0.5,
             precision: 4,
   
             where: "1 = 0"
   
           })
           .addTo(map);
   

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Execute the query

The parcels feature layer layer definition changes when you choose an option from the selector. You can access the chosen where clause with the value property of the select element.

1. Add a change event handler to the select element. Inside, use setWhere to change the layer definition.

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         const parcels = L.esri
           .featureLayer({
             url: "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/LA_County_Parcels/FeatureServer/0",
             simplifyFactor: 0.5,
             precision: 4,
   
             where: "1 = 0"
   
           })
           .addTo(map);
   
         const select = document.getElementById("whereClauseSelect");
         select.addEventListener("change", () => {
           if (select.value !== "") {
             parcels.setWhere(select.value);
           }
         });
   

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2. Create a pop-up using the bindPopup method. Set its contents dynamically based on the currently clicked feature.

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         const select = document.getElementById("whereClauseSelect");
         select.addEventListener("change", () => {
           if (select.value !== "") {
             parcels.setWhere(select.value);
           }
         });
   
         parcels.bindPopup(function (layer) {
             return L.Util.template("<b>Parcel {APN}</b>" + "Type: {UseType} <br>" + "Tax Rate City: {TaxRateCity}", layer.feature.properties);
         });
   
       </script>
   

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Run the app

In CodePen, run your code to display the map.

When the map displays, you should be able to use the query selector to display parcels. Click on a parcel to show a pop-up with the feature's attributes.

What's next?

Learn how to use additional ArcGIS location services in these tutorials: