Query features with SQL

Learn how to execute a SQL query to access polygon 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 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 hosted 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

You need an ArcGIS Developer or ArcGIS Online account to access the developer dashboard and create an API key.

Steps

Create a new pen

To get started, either complete the Display a map tutorial or .

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.

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

In CodePen, update apiKey to use your key.

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const apiKey = "YOUR_API_KEY";
const basemapId = "ArcGIS:Streets";
const basemapURL = "https://basemaps-api.arcgis.com/arcgis/rest/services/styles/" + basemapId + "?type=style&token=" + apiKey;
olms.apply(map, basemapURL);

Add references

This tutorial uses ArcGIS REST JS to query the feature layer, and the ol-popup library to display pop-ups.

In the <head> element, add references to the ArcGIS REST JS and ol-popup libraries.

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    <link rel="stylesheet" href="https://cdn.jsdelivr.net/gh/openlayers/openlayers.github.io@master/en/v6.15.1/css/ol.css" type="text/css" />
    <script src="https://cdn.jsdelivr.net/gh/openlayers/openlayers.github.io@master/en/v6.15.1/build/ol.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/ol-mapbox-style@10.5.0/dist/olms.js" type="text/javascript"></script>

    <script src="https://unpkg.com/@esri/arcgis-rest-request@4.0.0/dist/bundled/request.umd.js"></script>
    <script src="https://unpkg.com/@esri/arcgis-rest-feature-service@4.0.0/dist/bundled/feature-service.umd.js"></script>
    <script src="https://unpkg.com/ol-popup@4.0.0"></script>
    <link rel="stylesheet" href="https://unpkg.com/ol-popup@4.0.0/src/ol-popup.css" />
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Create a SQL selector

ArcGIS feature layers support a standard SQL query where clause. Use an HTML select element to provide a list of SQL queries for the LA County Parcel feature layer.

Create a select element containing an option element for each where clause.

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  <body>
    <div id="map"></div>

    <select id="query-select">
      <option value="" selected>Choose a WHERE clause...</option>
      <option value="UseType = 'Residential'">UseType = 'Residential'</option>
      <option value="UseType = 'Government'">UseType = 'Government'</option>
      <option value="UseType = 'Irrigated Farm'">UseType = 'Irrigated Farm'</option>
      <option value="TaxRateArea = 10853">TaxRateArea = 10853</option>
      <option value="TaxRateArea = 10860">TaxRateArea = 10860</option>
      <option value="TaxRateArea = 08637">TaxRateArea = 08637</option>
      <option value="Roll_LandValue > 1000000">Roll_LandValue &gt; 1000000</option>
      <option value="Roll_LandValue < 1000000">Roll_LandValue &lt; 1000000</option>
    </select>
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Add styling to position the select element in the top right.

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    <style>
      html,
      body,
      #map {
        padding: 0;
        margin: 0;
        height: 100%;
        width: 100%;
        font-family: Arial, Helvetica, sans-serif;
        font-size: 14px;
        color: #323232;
      }

      #query-select {
        position: absolute;
        top: 20px;
        right: 20px;
        padding: 4px 8px;
        font-size: 16px;
        border-radius: 0; /* Causes more uniform appearance across browsers. */
      }
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Add parcel layer

Parcels returned by the query are simple GeoJSON polygons. You will create a Vector layer to display them.

Add a load event handler to the olms function call. Inside, create a Vector layer and save it to a parcelLayer variable. Add it to the map with map.addLayer.

As you are not passing a style parameter, the default styling for polygons will be used. See the OpenLayers documentation for more details.

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      const basemapId = "ArcGIS:Streets";
      const basemapURL = "https://basemaps-api.arcgis.com/arcgis/rest/services/styles/" + basemapId + "?type=style&token=" + apiKey;

      const parcelLayer = new ol.layer.Vector();
      olms.apply(map, basemapURL).then((map) => {

        map.addLayer(parcelLayer);

      });
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Create the query

Use the ArcGIS REST JS queryFeatures method to find features in the LA County Parcels feature layer that match the selected where clause.

To limit the query results to the visible extent of the Map, you can set the queryFeatures geometry property. To do so your function will take a geometry object in the required esriGeometryEnvelope format of [minx, miny, maxx, maxy]. This confines the SQL query to the geographic bounds (extent) of the map.

When the matching parcels are returned, create a new Vector source using a GeoJSON feature format, to update your parcelsLayer Vector layer.

Create a function called executeQuery with whereClause and geometry parameters. Inside, create a new arcgisRest.ApiKeyManager to access the feature service. Call arcgisRest.queryFeatures. Pass the geometry and geometryType. Specify GeoJSON as the return type, requesting returnGeometry and specific outFields. All of the features within the geometry will be returned with attribute information set by the outFields property.

There are many other spatial relationships that you can specify with spatialRel. For example, you can use esriSpatialRelContains to only return parcels completely within the viewport. See the ArcGIS services reference for details.

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        map.addLayer(parcelLayer);

      });

      function executeQuery(whereClause, geometry) {
        arcgisRest
          .queryFeatures({
            url: "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/LA_County_Parcels/FeatureServer/0",
            geometry: geometry,
            geometryType: "esriGeometryEnvelope",
            inSR: 4326, // EPSG:4326 uses latitudes and longitudes
            spatialRel: "esriSpatialRelIntersects",
            where: whereClause,

            f: "geojson",
            returnGeometry: true,
            outFields: ["APN", "UseType", "TaxRateCity", " Roll_LandValue"]
          })

      }
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Add a response handler. Inside, create a GeoJSON feature format. Use it to read features from the response to a new Vector source.

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      function executeQuery(whereClause, geometry) {
        arcgisRest
          .queryFeatures({
            url: "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/LA_County_Parcels/FeatureServer/0",
            geometry: geometry,
            geometryType: "esriGeometryEnvelope",
            inSR: 4326, // EPSG:4326 uses latitudes and longitudes
            spatialRel: "esriSpatialRelIntersects",
            where: whereClause,

            f: "geojson",
            returnGeometry: true,
            outFields: ["APN", "UseType", "TaxRateCity", " Roll_LandValue"]
          })

          .then((response) => {
            const geojson = new ol.format.GeoJSON({
              defaultDataProjection: "EPSG:4326",
              featureProjection: "EPSG:3857"
            });

            let newSource = new ol.source.Vector({
              features: geojson.readFeatures(response)
            });
            parcelLayer.setSource(newSource);
          });

      }
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Execute the query

The executeQuery function needs to execute when you select an option from the select control. You achieve this by adding a change event handler. You can access the chosen where clause with the value property of the select element.

You need to calculate the extent of the current map view in latitude and longitude. You can use View.calculateExtent to get the extent, and proj.transformExtent to convert it to the EPSG:4326 spatial reference.

Add a change event handler to the select element. Inside, use View.calculateExtent and ol.proj.transformExtent to calculate the viewport extent. Call executeQuery with the extent and where clause.

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            let newSource = new ol.source.Vector({
              features: geojson.readFeatures(response)
            });
            parcelLayer.setSource(newSource);
          });

      }

      // Listen for changes
      const select = document.getElementById("query-select");
      select.addEventListener("change", () => {
        const whereClause = select.value;

        const extent3857 = map.getView().calculateExtent(map.getSize());
        const extent4326 = ol.proj.transformExtent(extent3857, "EPSG:3857", "EPSG:4326");
        executeQuery(whereClause, extent4326);
      });

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At the top right, click Run.

When you select a where clause using the select control, a query will run against the feature layer and display all land parcels within the current viewport matching the where clause.

Add a pop-up

The parcels returned from the query contain many attributes, such as land value and land use type. You can make the parcels interactive by showing a pop-up when the user clicks on a parcel. You create a Popup to display parcel attributes. It is a type of Overlay so you add it to the map with map.addOverlay.

Create a Popup and save it to a popup variable. Add it to the map with map.addOverlay.

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        const extent3857 = map.getView().calculateExtent(map.getSize());
        const extent4326 = ol.proj.transformExtent(extent3857, "EPSG:3857", "EPSG:4326");
        executeQuery(whereClause, extent4326);
      });

      const popup = new Popup();
      map.addOverlay(popup);
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Create a map click event handler. Inside, use map.getFeaturesAtPixel to get the clicked parcel, if any. If there is one, use popup.show to display a pop-up containing the parcel's APN, use type, land value and taxation city.

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      const popup = new Popup();
      map.addOverlay(popup);

      map.on("click", (event) => {
        const parcel = map.getFeaturesAtPixel(event.pixel, {
          layerFilter: (l) => l === parcelLayer // don't query layers from the basemap
        })[0];
        if (parcel) {
          const message =
            `<b>Parcel ${parcel.get("APN")}</b>` +
            `<br>Type: ${parcel.get("UseType")} <br>` +
            `Land value: ${parcel.get("Roll_LandValue")} <br>` +
            `Tax Rate City: ${parcel.get("TaxRateCity")}`;
          popup.show(event.coordinate, message);
        } else {
          popup.hide();
        }
      });
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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:

Query a feature layer (spatial)

Execute a spatial query to access polygon features from a feature service.

Get global data

Query demographic information for locations around the world with the GeoEnrichment service.

Get local data

Query regional facts, spending trends, and psychographics with the GeoEnrichment service.

Add a feature layer

Add features from feature layers to a map.

Style a feature layer

Use data-driven styling to apply symbol colors and styles to feature layers.

OpenLayers

Query features with SQL

Solution

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