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. Layers in OpenLayers can contain style functions, which use attribute values to change the appearance of features. This allows you to create complex, data-driven visualizations by relating visual variables to data attributes.
In this tutorial, you apply different styles to enhance the visualization of the Trailheads, Trails and Parks and Open Spaces feature layers.
Prerequisites
You need an ArcGIS Location Platform or ArcGIS Online account.
Steps
Create a new pen
- To get started, you can complete the Display a map tutorial or use the .
Get an access token
You need an access token with the correct privileges to access the resources used in this tutorial.
-
Go to the Create an API key tutorial and create an API key with the following 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.
- Privileges
-
Copy the API key access token to your clipboard when prompted.
-
In CodePen, update the
access
variable to use your access token.Token Use dark colors for code blocks const accessToken = "YOUR_ACCESS_TOKEN"; const basemapId = "arcgis/outdoor"; const basemapURL = `https://basemapstyles-api.arcgis.com/arcgis/rest/services/styles/v2/styles/${basemapId}?token=${accessToken}`; olms.apply(map, basemapURL);
-
Run the code to ensure the basemap is displayed in the map.
To learn about the other types of authentication available, go to Types of authentication.
Style trailheads with a hiker image and labels
A Style
in OpenLayers has several possible components: an image, text, stroke, fill and so on. To display a hiker icon for the trailheads layer, you use an Icon
style as the image
component. Specify which image file as the src
, and the size as the scale
parameter.
To display the trailhead name, you use a Text
style. Use a left
value for text
with an offset
of 10 to display the labels to the right of the icons. Use Fill
and Stroke
styles as the fill
and stroke
properties to give the labels white text with a teal outline. The font
property is a CSS font definition. Since the label for each trailhead is different, use a function to return a Style
for a given feature. Set the text
property using feature's TRL
attribute.
-
Inside
olms
load handler, create atrailhead
function that takes aStyle feature
and returns aStyle
containing anIcon
style. Usehttp
for the://static.arcgis.com/images/ Symbols/ NP S/nps Pictograph _0231b.png src
and set ascale
of 25%.ssssUse dark colors for code blocks const basemapId = "arcgis/outdoor"; const basemapURL = `https://basemapstyles-api.arcgis.com/arcgis/rest/services/styles/v2/styles/${basemapId}?token=${accessToken}`; olms.apply(map, basemapURL).then(function (map) { const trailheadStyle = function (feature) { return new ol.style.Style({ image: new ol.style.Icon({ src: "http://static.arcgis.com/images/Symbols/NPS/npsPictograph_0231b.png", scale: 0.25 }),
-
Add a
Text
style to display labels with white text, teal outline, in an italic sans-serif font. Set thetext
property using the feature'sTRL
attribute._NAME Use dark colors for code blocks const trailheadStyle = function (feature) { return new ol.style.Style({ image: new ol.style.Icon({ src: "http://static.arcgis.com/images/Symbols/NPS/npsPictograph_0231b.png", scale: 0.25 }), text: new ol.style.Text({ text: feature.get("TRL_NAME"), font: "italic 12px sans-serif", offsetX: 10, textAlign: "left", fill: new ol.style.Fill({ color: "#FFFFFF" }), stroke: new ol.style.Stroke({ color: "#5E8D74", width: 3 }) }) }); };
Add the Trailheads feature layer to the map
Use a Vector
layer with a Vector
source to display the trailheads.
For more information about adding feature layers using GeoJSON, see the Add a feature layer as GeoJSON tutorial.
-
Add a
Vector
layer with aVector
source to load and display the trailheads feature layer. Setdeclutter
to be true to prevent label overlap. Pass thetrailheads
function as theStyle style
property. Usemap.add
to add this layer to the map.Layer Use dark colors for code blocks stroke: new ol.style.Stroke({ color: "#5E8D74", width: 3 }) }) }); }; 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"; const trailheadsLayer = new ol.layer.Vector({ source: new ol.source.Vector({ format: new ol.format.GeoJSON(), url: trailheadsLayerURL, }), style: trailheadStyle, declutter: true }); map.addLayer(trailheadsLayer);
-
Add the data attribution for the feature layer source.
- Go to the Trailheads (Santa Monica Mountains) item.
- Scroll down to the Credits (Attribution) section and copy its value.
- Create an
attribution
property and paste the attribution value from the item.Use dark colors for code blocks stroke: new ol.style.Stroke({ color: "#5E8D74", width: 3 }) }) }); }; 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"; const trailheadsLayer = new ol.layer.Vector({ source: new ol.source.Vector({ format: new ol.format.GeoJSON(), url: trailheadsLayerURL, // Attribution text retrieved from https://arcgis.com/home/item.html?id=883cedb8c9fe4524b64d47666ed234a7 attributions: ['| Los Angeles GeoHub'] }), style: trailheadStyle, declutter: true }); map.addLayer(trailheadsLayer);
-
At the top right, click Run to test your map. You should see hiker icons and trailhead labels.
Style trail width by elevation gain
To visualize the elevation gain of a trail you can use the width of a Stroke
style. To do this, create another function which returns a Style
. The width
of the style's stroke
property will be a calculation converting feet of elevation gain to pixels of width.
-
Create a
trail
function that takes aStyle feature
and returns aStyle
with aStroke
style. Set thecolor
to pink, and calculate thewidth
property from the feature'sELEV
attribute._GAIN Use dark colors for code blocks style: trailheadStyle, declutter: true }); map.addLayer(trailheadsLayer); const trailStyle = function (feature) { return new ol.style.Style({ stroke: new ol.style.Stroke({ color: "#BA55D3", width: 3 + (4 * feature.get("ELEV_GAIN")) / 2300 }) }); };
-
Add the Trails feature layer as a
Vector
layer with a GeoJSONVector
source. Pass yourtrail
function as theStyle style
property. Useinsert
to add this layer below the trailheads layer.At Use dark colors for code blocks const trailStyle = function (feature) { return new ol.style.Style({ stroke: new ol.style.Stroke({ color: "#BA55D3", width: 3 + (4 * feature.get("ELEV_GAIN")) / 2300 }) }); }; 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"; const trailsLayer = new ol.layer.Vector({ source: new ol.source.Vector({ format: new ol.format.GeoJSON(), url: trailsLayerURL, }), style: trailStyle }); map.getLayers().insertAt(1, trailsLayer);
-
Add the data attribution for the feature layer source.
- Go to the Trails item.
- Scroll down to the Credits (Attribution) section and copy its value.
- Create an
attribution
property and paste the attribution value from the item.Use dark colors for code blocks const trailStyle = function (feature) { return new ol.style.Style({ stroke: new ol.style.Stroke({ color: "#BA55D3", width: 3 + (4 * feature.get("ELEV_GAIN")) / 2300 }) }); }; 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"; const trailsLayer = new ol.layer.Vector({ source: new ol.source.Vector({ format: new ol.format.GeoJSON(), url: trailsLayerURL, // Attribution text retrieved from https://arcgis.com/home/item.html?id=69e12682738e467eb509d8b54dc73cbd attributions: ['| Los Angeles GeoHub'] }), style: trailStyle }); map.getLayers().insertAt(1, trailsLayer);
-
At the top right, click Run to test your map. You should see the hiking trails in pink with thicker lines for those with more elevation gain.
Add a filtered bike-only trails layer
To display bike-only trails, you can add another style function to display a dashed line for trails that allow biking. You can display a dashed line by passing an array of alternating stroke and gap segments length as the line
property in a Stroke
style.
The same source from the trails
can be used.
-
Create a
bike
function. If the feature has aTrails Style Yes
value forUSE
, return a white dashed_BIKE Stroke
style. Otherwise, do not return aStyle
, so the feature will not be displayed.Use dark colors for code blocks style: trailStyle }); map.getLayers().insertAt(1, trailsLayer); const bikeTrailsStyle = function (feature) { if (feature.get("USE_BIKE") === "Yes") { return new ol.style.Style({ stroke: new ol.style.Stroke({ lineDash: [1, 4], color: "white", width: 2 }) }); } };
-
Add a
bike
using the source fromTrails Layer trails
, with theLayer bike
function. Insert the layer above theTrails Style trails
.Layer Use dark colors for code blocks stroke: new ol.style.Stroke({ lineDash: [1, 4], color: "white", width: 2 }) }); } }; const bikeTrailsLayer = new ol.layer.Vector({ source: trailsLayer.getSource(), style: bikeTrailsStyle }); map.getLayers().insertAt(2, bikeTrailsLayer);
-
At the top right, click Run to test your map. You should now see the bike-accessible trails with a dashed line.
Style a polygon layer
You can use color to communicate the category of a feature, such as the type of a park or open space. Use a style function to returns a Fill
style, in which you derive the color
property from the feature's TYPE
property.
-
Create a
parks
function which returns aStyle Fill
style. Look up the feature'sTYPE
attribute in a table to give a different color forNatural Areas
,Regionla Open Space
,Local Park
andRegional Recreation Park
. If the type is not one of these, make the color transparent.Use dark colors for code blocks const bikeTrailsLayer = new ol.layer.Vector({ source: trailsLayer.getSource(), style: bikeTrailsStyle }); map.getLayers().insertAt(2, bikeTrailsLayer); const parksStyle = function (feature) { const type = feature.get("TYPE"); const colorTable = { "Natural Areas": "#9E559C", "Regional Open Space": "#A7C636", "Local Park": "#149ECE", "Regional Recreation Park": "#ED5151" }; return new ol.style.Style({ fill: new ol.style.Fill({ color: colorTable[feature.get("TYPE")] || "transparent" }) }); };
-
Add the data attribution for the feature layer source.
- Go to the Parks and Open Space item.
- Scroll down to the Credits (Attribution) section and copy its value.
- Create an
attribution
property and paste the attribution value from the item.Use dark colors for code blocks const bikeTrailsLayer = new ol.layer.Vector({ source: trailsLayer.getSource(), style: bikeTrailsStyle }); map.getLayers().insertAt(2, bikeTrailsLayer); const parksStyle = function (feature) { const type = feature.get("TYPE"); const colorTable = { "Natural Areas": "#9E559C", "Regional Open Space": "#A7C636", "Local Park": "#149ECE", "Regional Recreation Park": "#ED5151" }; return new ol.style.Style({ fill: new ol.style.Fill({ color: colorTable[feature.get("TYPE")] || "transparent" }) }); };
-
Create a
Vector
layer with aVector
source for the parks feature layer. Pass yourparks
function as theStyle style
property, with a low opacity. Insert the parks layer below the trails layers.Use dark colors for code blocks return new ol.style.Style({ fill: new ol.style.Fill({ color: colorTable[feature.get("TYPE")] || "transparent" }) }); }; 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"; const parksLayer = new ol.layer.Vector({ source: new ol.source.Vector({ format: new ol.format.GeoJSON(), url: parksLayerURL, }), opacity: 0.2, style: parksStyle }); map.getLayers().insertAt(1, parksLayer);
Run the app
In CodePen, run your code to display the map.
You should now see parks of different colors, beneath the trails and trailhead layers.
What's next?
Learn how to use additional ArcGIS location services in these tutorials: