Style a feature layer

Learn how to use data-driven styling to apply symbol colors and styles to feature layers.

A feature layer is a dataset in a feature service hosted in ArcGIS. Each feature layer contains features with a single geometry type (point, line, or polygon), and a set of attributes. A feature layer can be styled in MapLibre GL JS with a layer connected to a GeoJSON source. Layers can contain expressions which use attribute values to calculate values. This lets you create complex, data-driven visualizations by relating visual variables to data attributes.

In this tutorial, you use symbol, line and fill layers to style three hosted feature layers in ArcGIS.

Prerequisites

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

Steps

Create a new pen

  1. 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.

  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 apiKey = "YOUR_API_KEY";
    const basemapEnum = "ArcGIS:Streets";
    const map = new maplibregl.Map({
      container: "map", // the id of the div element
      style: `https://basemaps-api.arcgis.com/arcgis/rest/services/styles/${basemapEnum}?type=style&token=${apiKey}`,
      zoom: 12, // starting zoom
      center: [-118.805, 34.027] // starting location [longitude, latitude]
    });
    

Load a hiker icon

To use an image as an icon, you must first load the image into the map style using map.loadImage and map.addImage.

  1. Call map.loadImage with 'https://static.arcgis.com/images/Symbols/NPS/npsPictograph_0231b.png' as the first parameter. The second parameter is a callback taking an error and the image.

    See the MapLibre GL JS documentation for more information.

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          const map = new maplibregl.Map({
            container: "map", // the id of the div element
            style: `https://basemaps-api.arcgis.com/arcgis/rest/services/styles/${basemapEnum}?type=style&token=${apiKey}`,
            zoom: 12, // starting zoom
            center: [-118.805, 34.027] // starting location [longitude, latitude]
          });
    
          map.loadImage("https://static.arcgis.com/images/Symbols/NPS/npsPictograph_0231b.png", (error, image) => {
    
          });
    
    Expand
  2. Call map.addImage to define hiker-icon as the provided image.

    A MapLibre style can contain a number of images as part of its sprite file. map.addImage is required to display images that are not included in its sprite file.

    See the MapLibre GL JS documentation for more information.

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          map.loadImage("https://static.arcgis.com/images/Symbols/NPS/npsPictograph_0231b.png", (error, image) => {
    
            if (error) {
              throw error;
            }
            map.addImage("hiker-icon", image);
    
          });
    
    Expand

Style and display trailheads with a hiker icon and labels

To display an icon of a hiker for each trailhead, along with a label, you can use a single symbol layer. Properties for the label start with text- and properties for the icon start with icon-.

  1. Create a function called showTrailheads. Inside, add a GeoJSON source.

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          map.loadImage("https://static.arcgis.com/images/Symbols/NPS/npsPictograph_0231b.png", (error, image) => {
    
            if (error) {
              throw error;
            }
            map.addImage("hiker-icon", image);
    
          });
    
          function showTrailheads() {
    
            const trailheadsLayerName = "Trailheads";
            const trailheadsLayerURL =
              "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/" +
              trailheadsLayerName +
              "/FeatureServer/0/query?where=1%3D1&outFields=*&returnGeometry=true&f=pgeojson";
            map.addSource("trailheads", {
              type: "geojson",
              data: trailheadsLayerURL
            });
    
          }
    
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  2. Add a symbol layer for the hiker icons. Use icon-image to reference the icon you loaded.

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          function showTrailheads() {
    
            const trailheadsLayerName = "Trailheads";
            const trailheadsLayerURL =
              "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/" +
              trailheadsLayerName +
              "/FeatureServer/0/query?where=1%3D1&outFields=*&returnGeometry=true&f=pgeojson";
            map.addSource("trailheads", {
              type: "geojson",
              data: trailheadsLayerURL
            });
    
            map.addLayer({
              id: "trailheads-symbol",
              type: "symbol",
              source: "trailheads",
              layout: {
                "icon-image": "hiker-icon",
                "icon-size": 0.3,
                "icon-allow-overlap": true,
    
              }
            });
    
          }
    
    Expand
  3. Add additional label properties. Set a text-anchor of bottom, with a text-offset of [0, -2] to position the label above the icon. Use the TRL_NAME attribute as the text field.

    For more information see the MapLibre GL JS documentation.

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            map.addLayer({
              id: "trailheads-symbol",
              type: "symbol",
              source: "trailheads",
              layout: {
                "icon-image": "hiker-icon",
                "icon-size": 0.3,
                "icon-allow-overlap": true,
    
                "text-font": ["Arial Italic"],
                "text-field": ["get", "TRL_NAME"],
                "text-size": 12,
                "text-anchor": "bottom",
                "text-offset": [0, -2]
    
              },
              paint: {
                "text-color": "white",
                "text-halo-color": "seagreen",
                "text-halo-width": 2
    
              }
            });
    
    Expand

Add a load event handler

It is important to wait for the MapLibre GL JS map to finish loading before adding any layers.

  1. Add an event handler to the map load event. Inside, call the showTrailheads function.

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              },
              paint: {
                "text-color": "white",
                "text-halo-color": "seagreen",
                "text-halo-width": 2
    
              }
            });
    
          }
    
          map.on("load", () => {
    
            showTrailheads();
    
          });
    
    Expand
  2. At the top right, click Run to test your map. You should see icons and labels at each of the trailheads.

Style and display all trails

  1. Create a showTrails function. Inside, add a GeoJSON source with id trails.

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              },
              paint: {
                "text-color": "white",
                "text-halo-color": "seagreen",
                "text-halo-width": 2
    
              }
            });
    
          }
    
          function showTrails() {
    
            const trailsLayerName = "Trails";
            const trailsLayerURL =
              "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/" +
              trailsLayerName +
              "/FeatureServer/0/query?where=1%3D1&outFields=*&returnGeometry=true&f=pgeojson";
            map.addSource("trails", {
              type: "geojson",
              data: trailsLayerURL
            });
    
          }
    
    Expand
  2. Add a line layer with id trails-line to display the trails source.

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          function showTrails() {
    
            const trailsLayerName = "Trails";
            const trailsLayerURL =
              "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/" +
              trailsLayerName +
              "/FeatureServer/0/query?where=1%3D1&outFields=*&returnGeometry=true&f=pgeojson";
            map.addSource("trails", {
              type: "geojson",
              data: trailsLayerURL
            });
    
            map.addLayer({
              id: "trails-line",
              type: "line",
              source: "trails",
              paint: {
                "line-color": "hsl(291, 44%, 60%)",
    
                "line-opacity": 0.75
              }
            });
    
          }
    
    Expand
  3. At the top right, click Run to test your map. The trails should display as purple lines.

Style trail width by elevation gain

To make the width of the trail line reflect the elevation gain, you can use a MapLibre GL expression as the value of the line-width. You use the ['interpolate'] and ['get'] expressions to achieve this.

['interpolate', ['linear'], ... creates a linear mapping from one range of input values (the number of feet of elevation gain) to a range of output values (the number of pixels of line width). You provide "stops", such as mapping 2,300 feet to 7 pixels. See the MapLibre Style Specification for details.

['get', 'ELEV_GAIN'] accesses the ELEV_GAIN property. See the MapLibre Style Specification for details.

  1. Update the trails-line layer definition that calculates line-width from the ELEV_GAIN attribute.

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            map.addLayer({
              id: "trails-line",
              type: "line",
              source: "trails",
              paint: {
                "line-color": "hsl(291, 44%, 60%)",
    
                "line-width": ["interpolate", ["linear"], ["get", "ELEV_GAIN"], 0, 3, 2300, 7],
    
                "line-opacity": 0.75
              }
            });
    
    Expand
  2. At the top right, click Run to test your map. The trails should display as purple lines with varying thickness based on elevation gain.

Display bike-only trails

You can limit a layer to display only certain features by setting a filter. A filter is defined by an expression that should evaluate to true for the features you want included.

To show trails that allow bikes with a dashed line, you can create a new layer that sits above the other trails layer. You can reuse the existing source.

  1. Create a function called showBikeTrails. Inside, add a layer with id biketrails-line. Use a filter to only show trails where USE_BIKE has a value of YES. Set line-dasharray to [1, 2] to create short dashes.

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            map.addLayer({
              id: "trails-line",
              type: "line",
              source: "trails",
              paint: {
                "line-color": "hsl(291, 44%, 60%)",
    
                "line-width": ["interpolate", ["linear"], ["get", "ELEV_GAIN"], 0, 3, 2300, 7],
    
                "line-opacity": 0.75
              }
            });
    
          }
    
          function showBikeTrails() {
    
            map.addLayer({
              id: "biketrails-line",
              type: "line",
              source: "trails",
              filter: ["==", ["get", "USE_BIKE"], "Yes"],
              paint: {
                "line-dasharray": [1, 2],
                "line-width": 2,
                "line-color": "hsl(300, 100%, 78.4%)"
              }
            });
    
          }
    
    Expand
  2. In the load event handler, call the showTrails and showBikeTrails functions. Add the calls before showTrailheads so that the trails layers are placed beneath the trailheads.

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          map.on("load", () => {
    
            showTrails();
            showBikeTrails();
    
            showTrailheads();
    
          });
    
    Expand
  3. At the top right, click Run to test your map. The trails should appear as dashed lines for trails that allow bikes.

Display park areas with different colors

You can use a different style for each unique attribute value in a feature layer. Use a ['match', ...] expression to display park polygons with different colors depending on the TYPE field.

A ['match', ...] expression choose between several different output values depending on the input value. See the MapLibre Style Specification for details.

  1. Create a function called showParks. Inside, add a GeoJSON source for the parks. Give it an id of parks.

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            map.addLayer({
              id: "biketrails-line",
              type: "line",
              source: "trails",
              filter: ["==", ["get", "USE_BIKE"], "Yes"],
              paint: {
                "line-dasharray": [1, 2],
                "line-width": 2,
                "line-color": "hsl(300, 100%, 78.4%)"
              }
            });
    
          }
    
          function showParks() {
    
            const parksLayerName = "Parks_and_Open_Space";
            const parksLayerURL =
              "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/" +
              parksLayerName +
              "/FeatureServer/0/query?where=1%3D1&outFields=*&returnGeometry=true&f=pgeojson";
            map.addSource("parks", {
              type: "geojson",
              data: parksLayerURL
            });
    
          }
    
    Expand
  2. Add a fill layer with id parks-fill and source parks. For the fill color, use a match expression for different TYPE values.

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          function showParks() {
    
            const parksLayerName = "Parks_and_Open_Space";
            const parksLayerURL =
              "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/" +
              parksLayerName +
              "/FeatureServer/0/query?where=1%3D1&outFields=*&returnGeometry=true&f=pgeojson";
            map.addSource("parks", {
              type: "geojson",
              data: parksLayerURL
            });
    
            map.addLayer({
              id: "parks-fill",
              type: "fill",
              source: "parks",
              paint: {
                "fill-color": [
                  "match",
                  ["get", "TYPE"],
                  "Natural Areas",
                  "#9E559C",
                  "Regional Open Space",
                  "#A7C636",
                  "Local Park",
                  "#149ECE",
                  "Regional Recreation Park",
                  "#ED5151",
                  "black"
                ],
                "fill-opacity": 0.2
              }
            });
    
          }
    
    Expand
  3. Back inside the load event handler, call the showParks functions. Place it before the other functions so that the parks layer is placed under the trails and trailheads.

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          map.on("load", () => {
    
            showParks();
    
            showTrails();
            showBikeTrails();
    
            showTrailheads();
    
          });
    
    Expand

Run the app

In CodePen, run your code to display the map.

You should now see trailheads with icons and labels, trails whose width varies by elevation, dashed lines for trails that allow bikes, and parks of different colors.

What's next?

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

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