Query a feature layer (SQL) | MapLibre GL JS

Learn how to query a feature layer with SQL.

Query a feature layer with SQL using API key authentication

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.

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 resulting features are displayed as graphics on the map. A pop-up is also used to display feature attributes.

Prerequisites

You need an ArcGIS Location Platform or ArcGIS Online account.

Steps

Get the starter app

Select a type of authentication and follow the steps to create a new app.

Choose API key authentication if you:

Want the easiest way to get started.
Want to build public applications that access ArcGIS Location Services and secure items.
Have an ArcGIS Location Platform or ArcGIS Online account.

Choose user authentication if you:

Want to build private applications.
Require application users to sign in with their own ArcGIS account and access resources their behalf.
Have an ArcGIS Online account.

To learn more about both types of authentication, go to Authentication.

You can choose one of the following to create a new CodePen:

Option 1: Complete the Display a map tutorial; or,
Option 2: Start from the Display a map tutorial .

Set up authentication

Create a new API key credential with the correct privileges to get an access token.

Go to the Create an API key tutorial to follow the steps to get an access token with these privilege(s):
- Privileges
  - Location services > Basemaps
- Item access
  - Note: If you are using your own custom data layer for this tutorial, you need to grant the API key credentials access to the layer item. Learn more in Item access privileges.

Set developer credentials

Use the API key or OAuth developer credentials so your application can access ArcGIS services.

Update the accessToken variable to use your API key.

Expand
Use dark colors for code blocks
    /* Use for API key authentication */
    const accessToken = "YOUR_ACCESS_TOKEN";
Expand

In both the index.html and callback.html files, replace YOUR_CLIENT_ID and YOUR_REDIRECT_URL with the client ID and redirect URL of your OAuth credentials.

index.html
Use dark colors for code blocks
    /* Use for user authentication */
    const clientId = "YOUR_CLIENT_ID"; // Your client ID from OAuth credentials
    const redirectUri = ""YOUR_REDIRECT_URI""; // The redirect URL registered in your OAuth credentials
    const session = await arcgisRest.ArcGISIdentityManager.beginOAuth2({
      clientId,
      redirectUri,
      portal: "https://www.arcgis.com/sharing/rest" // Your portal URL
    });

    const accessToken = session.token;

callback.html
Use dark colors for code blocks
    arcgisRest.ArcGISIdentityManager.completeOAuth2({
      clientId: "YOUR_CLIENT_ID", // Your client ID from OAuth credentials
      redirectUri: "YOUR_REDIRECT_URI", // The redirect URL registered in your OAuth credentials
      portal: "https://www.arcgis.com/sharing/rest" // Your portal URL
    });

Run the app and ensure you can sign in successfully.

If you are unable to sign in, make sure you have the correct redirect URL and port. This URL varies based on your application and typically takes the format of https://<server>[:port]/callback.html or http://my-arcgis-app:/auth. For example, if you are running an application on http://127.0.0.1:5500/, set http://127.0.0.1:5500/callback.html as your redirect URL in the index.html and callback.html file and your developer credential. They all have to match!

Add script references

This tutorial uses ArcGIS REST JS to query the feature layer.

In the <head> element, add references to the ArcGIS REST JS library.

Expand
Use dark colors for code blocks
    <!-- Load MapLibre GL JS from CDN -->
    <script src="https://unpkg.com/maplibre-gl@5.10.0/dist/maplibre-gl.js"></script>
    <link href="https://unpkg.com/maplibre-gl@5.10.0/dist/maplibre-gl.css" rel="stylesheet">
    <!-- Load MapLibre ArcGIS from CDN -->
    <script src="https://unpkg.com/@esri/maplibre-arcgis@1.0.0/dist/umd/maplibre-arcgis.min.js"></script>

    <script src="https://unpkg.com/@esri/arcgis-rest-request@4/dist/bundled/request.umd.js"></script>
    <script
      src="https://unpkg.com/@esri/arcgis-rest-feature-service@4/dist/bundled/feature-service.umd.js"></script>

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

    </style>
  </head>
Expand

Create a SQL selector

Hosted 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.

To add the <select> HTML element as a Map control, you create an object that implements the MapLibre GL JS IControl interface.

Creating an IControl allows MapLibre GL JS to position it, which prevents your control overlapping other MapLibre GL JS controls.

Create a QueryControl class with an onAdd function. Inside, create a <div> element with a <select> inside, with options for each of the SQL where clauses. Return this element.

Expand
Use dark colors for code blocks
    const map = new maplibregl.Map({
      container: "map", // the id of the div element
      zoom: 12, // starting zoom

      center: [-118.80543, 34.03] // starting location [longitude, latitude]

    });
    const basemapStyle = maplibreArcGIS.BasemapStyle.applyStyle(map, {
      style: "arcgis/outdoor",
      token: accessToken
    });

    class QueryControl {
      onAdd(map) {
        const template = document.createElement("template");
        template.innerHTML = `<div class="maplibregl-ctrl maplibregl-ctrl-group" style="margin:20px;">
            <select style="font-size:16px; padding:4px 8px;">
              <option value="">Choose a WHERE clause...</option>
              <option>UseType = 'Residential'</option>
              <option>UseType = 'Government'</option>
              <option>UseType = 'Irrigated Farm'</option>
              <option>TaxRateArea = 10853</option>
              <option>TaxRateArea = 10860</option>
              <option>TaxRateArea = 08637</option>
              <option>Roll_LandValue > 1000000</option>
              <option>Roll_LandValue < 1000000</option>
            </select>
          </div>`;

        return template.content;
      }
    }
Expand

Create a QueryControl and add it to the Map with map.addControl.

Expand
Use dark colors for code blocks
        return template.content;
      }
    }

    const queryControl = new QueryControl();
    map.addControl(queryControl);
Expand

Add parcel layer

Parcels returned by the query are simple GeoJSON polygons. You can display them with a GeoJSON source and a fill layer.

Create an addParcelLayer function. Inside, add a GeoJSON source and a fill layer. Add the layer before the first symbol layer.

By inserting the polygon layer beneath the icon and text layers, it keeps the labels readable. In MapLibre GL JS, there is no distinction between "basemap" layers and "overlay layers", so you can insert the layer anywhere.

To determine the first symbol layer, you can use map.getStyle to get the style, then iterate to find the first layer whose type is symbol.

See the MapLibre GL JS documentation for details.

Expand
Use dark colors for code blocks
    const queryControl = new QueryControl();
    map.addControl(queryControl);

    function addParcelLayer() {
      map.addSource("parcels", {
        type: "geojson",
        data: {
          type: "FeatureCollection",
          features: []
        },

      });

      const firstSymbolLayer = map.getStyle().layers.find((l) => l.type === "symbol");
      map.addLayer(
        {
          id: "parcels-fill",
          source: "parcels",
          type: "fill",
          paint: {
            "fill-color": "hsla(200, 80%,50%, 0.5)",

            "fill-outline-color": "hsl(360, 100%, 100%)"
          }
        },
        firstSymbolLayer.id
      ); // insert new layer before this one
      map.addLayer({
        id: "parcels-line",
        source: "parcels",
        type: "line",
        paint: {
          "line-width": 0.5,
          "line-color": "hsl(360, 100%,100%)"
        }
      }); // set outline style for parcels
    }
Expand

Add the data attribution for the feature layer source.

Go to the LA County Parcels item.
Scroll down to the Acknowledgments section and copy its value.

Paste the copied value to the attribution property.

Expand
Use dark colors for code blocks
    const queryControl = new QueryControl();
    map.addControl(queryControl);

    function addParcelLayer() {
      map.addSource("parcels", {
        type: "geojson",
        data: {
          type: "FeatureCollection",
          features: []
        },

        // Attribution text retrieved from https://arcgis.com/home/item.html?id=a6fdf2ee0e454393a53ba32b9838b303
        attribution: "LA County Parcels"

      });

      const firstSymbolLayer = map.getStyle().layers.find((l) => l.type === "symbol");
      map.addLayer(
        {
          id: "parcels-fill",
          source: "parcels",
          type: "fill",
          paint: {
            "fill-color": "hsla(200, 80%,50%, 0.5)",

            "fill-outline-color": "hsl(360, 100%, 100%)"
          }
        },
        firstSymbolLayer.id
      ); // insert new layer before this one
      map.addLayer({
        id: "parcels-line",
        source: "parcels",
        type: "line",
        paint: {
          "line-width": 0.5,
          "line-color": "hsl(360, 100%,100%)"
        }
      }); // set outline style for parcels
    }
Expand

Add load handler

To add layers to the map, you need to use the load event to ensure the map is fully loaded.

Add an event handler for the load event. Inside, call addParcelLayer.

Expand
Use dark colors for code blocks
      const firstSymbolLayer = map.getStyle().layers.find((l) => l.type === "symbol");
      map.addLayer(
        {
          id: "parcels-fill",
          source: "parcels",
          type: "fill",
          paint: {
            "fill-color": "hsla(200, 80%,50%, 0.5)",

            "fill-outline-color": "hsl(360, 100%, 100%)"
          }
        },
        firstSymbolLayer.id
      ); // insert new layer before this one
      map.addLayer({
        id: "parcels-line",
        source: "parcels",
        type: "line",
        paint: {
          "line-width": 0.5,
          "line-color": "hsl(360, 100%,100%)"
        }
      }); // set outline style for parcels
    }

    map.on("load", () => {

      addParcelLayer();

    });
Expand

Execute 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 geometry property. This confines the SQL query to the geographic bounds (extent) of the map.

When the matching parcels are returned, call setData on the parcels source to display them.

Create a function that calls arcgisRest.queryFeatures. 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.

Expand
Use dark colors for code blocks
    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"]
        })

    }
Expand

Add a response handler. Inside, set the returned parcels as the data for the parcels source.

Expand
Use dark colors for code blocks
      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) => {
          map.getSource("parcels").setData(response);
        });
Expand

Update your QueryControl to add a change event handler to the select element. Inside, calculate the viewport extent and call executeQuery with the extent and where clause.

Expand
Use dark colors for code blocks
    class QueryControl {
      onAdd(map) {
        const template = document.createElement("template");
        template.innerHTML = `<div class="maplibregl-ctrl maplibregl-ctrl-group" style="margin:20px;">
            <select style="font-size:16px; padding:4px 8px;">
              <option value="">Choose a WHERE clause...</option>
              <option>UseType = 'Residential'</option>
              <option>UseType = 'Government'</option>
              <option>UseType = 'Irrigated Farm'</option>
              <option>TaxRateArea = 10853</option>
              <option>TaxRateArea = 10860</option>
              <option>TaxRateArea = 08637</option>
              <option>Roll_LandValue > 1000000</option>
              <option>Roll_LandValue < 1000000</option>
            </select>
          </div>`;

        const select = template.content.querySelector("select");
        select.addEventListener("change", () => {
          // Do nothing for the "Choose a WHERE clause..." option
          if (select.value !== "") {
            // Get bounds in [minx, miny, maxx, maxy] format
            const bounds = map.getBounds().toArray().flat();
            executeQuery(select.value, bounds);
          }
        });

        return template.content;
      }
    }
Expand

At the top right, click Run. When you select a where clause using the toolbox, 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

You can add a Popup to view attributes of a parcel when the user clicks on it.

Add a click event handler to the parcels-fill layer. Inside, create a popup that display the attributes of the clicked parcel. Set the position of the pop-up and add it to the map.

Expand
Use dark colors for code blocks
        .then((response) => {
          map.getSource("parcels").setData(response);
        });

    }

    map.on("click", "parcels-fill", (e) => {
      const parcel = e.features[0].properties;
      const landValue = parcel.Roll_LandValue != "null" ? `$${parcel.Roll_LandValue.toLocaleString()}` : "N/A";
      const message =
        `<b>Parcel ${parcel.APN}</b></br>` +
        `Type: ${parcel.UseType} <br>` +
        `Land value: ${landValue} <br>` +
        `Tax Rate City: ${parcel.TaxRateCity}`;

      new maplibregl.Popup().setHTML(message).setLngLat(e.lngLat).addTo(map);
    });
Expand

Run the app

Run the app.

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 attributes.