Display a pop-up

Learn how to display feature attributes in a pop-up.

A pop-up, also known as a "popup", is a visual element that displays information about a feature when it is clicked. You typically style and configure a pop-up using HTML and CSS for each layer in a map. Pop-ups can display attribute values, calculated values, or rich content such as images, charts, or videos.

In this tutorial, you create an interactive pop-up for the Trailheads feature layer in the Santa Monica Mountains. When a feature is clicked, a pop-up is displayed containing the name of the trail and the service that manages it. You use the ol-popup library to achieve this.

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 the pop-up library

OpenLayers does not include a pop-up component. You can use the third-party library ol-popup to simplify adding pop-ups to your map.

In the <head> element, add references to the ol-popup library.

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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/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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Add the trailheads layer

Use a Vector layer with a Vector source to display the trailheads as GeoJSON.

For more information about adding feature layers using GeoJSON, see the Add a feature layer as GeoJSON tutorial.

Before the olms initialization, create a a Vector layer. Give it a Vector source with a GeoJSON feature format to load and display the trailheads feature layer. Save it to a trailheadsLayer variable.

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      const basemapId = "ArcGIS:Streets";

      const trailheadsLayer = new ol.layer.Vector({
        source: new ol.source.Vector({
          format: new ol.format.GeoJSON(),
          url: `https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/Trailheads/FeatureServer/0/query?where=1%3D1&outFields=*&returnGeometry=true&f=pgeojson`
        })
      });
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Add a load handler to the olms initialization. Inside, Use map.addLayer to add this layer to the map.

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

        .then(function (map) {
          map.addLayer(trailheadsLayer);
        });
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Initialize the pop-up

A Popup is a type of Overlay. Use map.addOverlay to add it to the map.

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

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        .then(function (map) {
          map.addLayer(trailheadsLayer);
        });

      const popup = new Popup();
      map.addOverlay(popup);
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Display a pop-up on click

A pop-up can display any HTML content. Use a click event handler to detect the click, then use map.getFeaturesAtPixel to find any trailhead features at the clicked point. You pass a function as a layerFilter to do so.

If the returned array contains at least one feature, you can use Feature.get to extract the trail name (TRL_NAME) and park name (PARK_NAME). You then use popup.show to update the pop-up position and content.

Add a click event handler. Inside, use getFeaturesAtPixel to get an array of trailhead features clicked on.

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

      map.on("click", (event) => {
        let trailName, parkName;

        const trailheads = map.getFeaturesAtPixel(event.pixel, {
          layerFilter: (layer) => layer === trailheadsLayer
        });

      });
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If there is a trail name to show, use popup.show to set the position and content of the pop-up. Otherwise, use popup.hide to hide it.

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        const trailheads = map.getFeaturesAtPixel(event.pixel, {
          layerFilter: (layer) => layer === trailheadsLayer
        });

        if (trailheads.length > 0) {

          const trailName = trailheads[0].get("TRL_NAME");
          const parkName = trailheads[0].get("PARK_NAME");
          popup.show(event.coordinate, `<b>${trailName}</b></br>${parkName}`);

        } else {
          popup.hide();
        }
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Run the app

In CodePen, run your code to display the map.

The map view should display the Trailheads feature layer. When you click a feature, the name of the trailhead and its park name is displayed in a pop-up.