Query a feature layer (spatial)

Learn how to execute a spatial query to access features from 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 either a SQL or spatial query, or both at the same time. You can return feature attributes, geometry, or both attributes and geometry for each record. SQL and spatial queries are useful when you want to access just a subset of your hosted data.

In this tutorial, you will use the Sketch widget to draw a feature and then perform a spatial query against a feature layer. The query layer is the LA County Parcels feature layer containing ±2.4 million features. The spatial query uses the sketched feature to return all of the parcels that intersect.

Prerequisites

Steps

Create a new pen

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

Get an access token

You need an access token with the correct privileges to access the location services used in this tutorial.

1. Go to the Create an API key tutorial and create an API key with the following privilege(s):
   
   • Privileges
     • Location services > Basemaps
2. In CodePen, set esriConfig.apiKey to your API key..
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   esriConfig.apiKey = "YOUR_ACCESS_TOKEN";
   const map = new Map({
     basemap: "arcgis/topographic" // basemap styles service
   });

To learn about other ways to get an access token, go to Types of authentication.

Add modules

1. In the require statement, add the Sketch, GraphicsLayer, and FeatureLayer modules.
   More info

   The ArcGIS Maps SDK for JavaScript is available as AMD modules and ES modules, but this tutorial is based on AMD. The AMD require function uses references to determine which modules will be loaded – for example, you can specify "esri/Map" for loading the Map module. After the modules are loaded, they are passed as parameters (e.g. Map) to the callback function where they can be used in your application. It is important to keep the module references and callback parameters in the same order. To learn more about the API's different modules visit the Overview Guide page.

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         "esri/config",
         "esri/Map",
         "esri/views/MapView",
   
         "esri/widgets/Sketch",
         "esri/layers/GraphicsLayer",
         "esri/layers/FeatureLayer"
   
       ], function(esriConfig, Map, MapView, Sketch, GraphicsLayer, FeatureLayer) {
   

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Create a sketch widget

Use the Sketch and GraphicsLayer classes to create a graphic. The graphic will be added to the map in a graphics layer. The event handler will listen for a change from the sketch widget and update the query accordingly.

1. Create a graphicsLayerSketch and add it to the map.

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         const view = new MapView({
           container: "viewDiv",
           map: map,
           center: [-118.80543,34.03000], //Longitude, latitude
           zoom: 13
         });
   
         // Add sketch widget
         const graphicsLayerSketch = new GraphicsLayer();
         map.add(graphicsLayerSketch);
   

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2. Create a sketch widget and set the layer property to graphicsLayerSketch. Add the widget to the top-right of the view.

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         // Add sketch widget
         const graphicsLayerSketch = new GraphicsLayer();
         map.add(graphicsLayerSketch);
   
         const sketch = new Sketch({
           layer: graphicsLayerSketch,
           view: view,
           creationMode: "update" // Auto-select
         });
   
         view.ui.add(sketch, "top-right");
   

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3. Create an event listener that will update each time a graphic is drawn. This will run a new query.

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         view.ui.add(sketch, "top-right");
   
         // Add sketch events to listen for and execute query
         sketch.on("update", (event) => {
   
         });
   

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4. You should see the sketch widget at the top right of the view. Click on one of the options in the widget to draw on the map.

Create a feature layer to query

Use the FeatureLayer class to perform a query against the LA County Parcels feature layer. Since you are performing a server-side query, the feature layer does not need to be added to the map.

1. Create a parcelLayer and set the url property to access the feature layer in the feature service.

   More info

   Feature layers are referenced by an index number at the end of the url. To determine the index number, visit the LA County Parcels feature service. In this case the index is 0.

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         // Add sketch events to listen for and execute query
         sketch.on("update", (event) => {
   
         });
   
         // Reference query layer
         const parcelLayer = new FeatureLayer({
           url: "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/LA_County_Parcels/FeatureServer/0",
         });
   

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Execute the query

Define a parcelQuery and use the FeatureLayer queryFeatures method to execute a query.

1. Create a queryFeaturelayer function with geometry as a parameter and define parcelQuery. Set the spatialRelationship to intersects and use the geometry from the sketch widget. Limit the attributes returned by setting the outFields property to a list of fields. Lastly, set returnGeometry to true so the feature geometriescan be displayed.

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         // Reference query layer
         const parcelLayer = new FeatureLayer({
           url: "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/LA_County_Parcels/FeatureServer/0",
         });
   
         function queryFeaturelayer(geometry) {
   
           const parcelQuery = {
            spatialRelationship: "intersects", // Relationship operation to apply
            geometry: geometry,  // The sketch feature geometry
            outFields: ["APN","UseType","TaxRateCity","Roll_LandValue"], // Attributes to return
            returnGeometry: true
           };
   
         }
   

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2. Call the queryFeatures method on the parcelLayer using the parameters defined in the parcelQuery element. To view the number of features returned, write the result length to the console. This will be updated in the next step.

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         function queryFeaturelayer(geometry) {
   
           const parcelQuery = {
            spatialRelationship: "intersects", // Relationship operation to apply
            geometry: geometry,  // The sketch feature geometry
            outFields: ["APN","UseType","TaxRateCity","Roll_LandValue"], // Attributes to return
            returnGeometry: true
           };
   
           parcelLayer.queryFeatures(parcelQuery)
           .then((results) => {
   
             console.log("Feature count: " + results.features.length)
   
           }).catch((error) => {
             console.log(error);
           });
   
         }
   

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3. Update the event handler to call the queryFeatureLayer function every time a graphic is sketched on the map. It will also listen for any reshape or move changes made to the graphic.

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         // Add sketch events to listen for and execute query
         sketch.on("update", (event) => {
   
           // Create
           if (event.state === "start") {
             queryFeaturelayer(event.graphics[0].geometry);
           }
           if (event.state === "complete"){
             graphicsLayerSketch.remove(event.graphics[0]); // Clear the graphic when a user clicks off of it or sketches new one
           }
           // Change
           if (event.toolEventInfo && (event.toolEventInfo.type === "scale-stop" || event.toolEventInfo.type === "reshape-stop" || event.toolEventInfo.type === "move-stop")) {
             queryFeaturelayer(event.graphics[0].geometry);
           }
   
         });
   

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4. Use the widget to draw a graphic. At the bottom left, click Console to view the number of features returned from the query.

Display features

To display the parcel features returned from the query, add them to the view as polygon graphics. Before the graphics are added, define a symbol and a pop-up so that the attributes can be displayed when a feature is clicked.

1. Create a displayResults function. Define a symbol and popupTemplate variable to style and display a pop-up for polygon graphics. The attributes referenced match the outFields specified in the query earlier.

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           const parcelQuery = {
            spatialRelationship: "intersects", // Relationship operation to apply
            geometry: geometry,  // The sketch feature geometry
            outFields: ["APN","UseType","TaxRateCity","Roll_LandValue"], // Attributes to return
            returnGeometry: true
           };
   
         }
   
         // Show features (graphics)
         function displayResults(results) {
   
         // Create a blue polygon
           const symbol = {
             type: "simple-fill",
             color: [ 20, 130, 200, 0.5 ],
             outline: {
               color: "white",
               width: .5
             },
           };
   
           const popupTemplate = {
             title: "Parcel {APN}",
             content: "Type: {UseType} <br> Land value: {Roll_LandValue} <br> Tax Rate City: {TaxRateCity}"
           };
   
         }
   

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2. Assign the symbol and popupTemplate elements to each feature returned from the query.

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           const popupTemplate = {
             title: "Parcel {APN}",
             content: "Type: {UseType} <br> Land value: {Roll_LandValue} <br> Tax Rate City: {TaxRateCity}"
           };
   
           // Set symbol and popup
           results.features.map((feature) => {
             feature.symbol = symbol;
             feature.popupTemplate = popupTemplate;
             return feature;
           });
   

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3. Clear the existing graphics and pop-up, and then add the new features to the view as graphics.

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           // Set symbol and popup
           results.features.map((feature) => {
             feature.symbol = symbol;
             feature.popupTemplate = popupTemplate;
             return feature;
           });
   
           // Clear display
           view.closePopup();
           view.graphics.removeAll();
          // Add features to graphics layer
           view.graphics.addMany(results.features);
   

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4. Update the queryFeaturelayer function to call the displayResults function. Remove the console.log.

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           parcelLayer.queryFeatures(parcelQuery)
           .then((results) => {
   
             console.log("Feature count: " + results.features.length)
   
             displayResults(results);
   

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Run the app

In CodePen, run your code to display the map.

When you use the widget to sketch a feature on the map, the spatial query runs against the feature layer and returns all parcels that intersect the sketched feature.

What's next?

Learn how to use additional API features and ArcGIS services in these tutorials:

• Query a feature layer (SQL)
• Edit feature data
• Import data as a feature layer