Find the elevations of multiple points

Learn how to find elevation values for points along a path in New Zealand's South Island.

The ArcGIS Elevation service is a location service that returns elevation values for a single location or multiple locations. Elevation coverage is provided for both topography (land elevations) and bathymetry (water depths) and takes location inputs as longitude and latitude coordinates.

In this tutorial, use the MapLibre ArcGIS plugin to display a map and ArcGIS REST JS to access the Elevation service and get elevation values for points along a path in New Zealand's South Island. The values will be returned as measures above mean sea level in meters.

Prerequisites

Steps

Get the starter app

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

Set up authentication

Set developer credentials

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

Update the map

1. Set the basemap to arcgis/topographic display topographic details.

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

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2. To focus on South Island, New Zealand, update the map's center to 169.0016, -44.6323 and set the zoom level to 10.

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       const map = new maplibregl.Map({
         container: "map",
   
         zoom: 10,
         center: [169.0016, -44.6323]
   
       });
   

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Define points of interest

You need to define the coordinates of interest from Kingston to Frankton in New Zealand's South Island, passing through the Lake Wakatipu. You then draw a polyline connecting these points to visualize the route on the map.

1. Define a set of points starting from Kingston, passing through Lake Wakatipu, and reaching Frankton.

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       const points = [
         [168.957299, -44.665736],
         [168.970268, -44.655672],
         [168.993555, -44.645187],
         [169.007703, -44.630505],
         [168.999450, -44.609314],
         [169.026863, -44.610783],
         [169.056045, -44.609104]
       ];
   

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2. Draw a line to connect the points and add it to the map.

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       map.once("load", () => {
         const coordinates = points.map(([lng, lat]) => [lng, lat]);
   
         map.addSource("line", {
           type: "geojson",
           data: {
             type: "Feature",
             geometry: {
               type: "LineString",
               coordinates: coordinates
             }
           }
         });
   
         map.addLayer({
           id: "line",
           type: "line",
           source: "line"
         });
   
       });
   

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3. Using Marker raw a marker on each point and add it to the map.

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       map.once("load", () => {
         const coordinates = points.map(([lng, lat]) => [lng, lat]);
   
         map.addSource("line", {
           type: "geojson",
           data: {
             type: "Feature",
             geometry: {
               type: "LineString",
               coordinates: coordinates
             }
           }
         });
   
         map.addLayer({
           id: "line",
           type: "line",
           source: "line"
         });
   
         coordinates.forEach(([lng, lat]) => {
           new maplibregl.Marker()
             .setLngLat([lng, lat])
             .addTo(map);
         });
   
       });
   

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Get elevation data

After defining the points and drawing the route, make a request to the Elevation service to get the elevations of the points along the route.

1. Define a function called fetchElevationData() and call it.

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       async function fetchElevationData() {
   
       }
   

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2. Use ArcGIS REST JS findElevationAtManyPoints method to call the Elevation service and pass in the array of points.

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       async function fetchElevationData() {
   
         const data = await arcgisRest.findElevationAtManyPoints({
           coordinates: points,
           authentication: arcgisRest.ApiKeyManager.fromKey(accessToken)
         });
   
       }
   

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Display results

Once the elevation data is fetched, you can display the results on the map. This involves extracting the elevation values from the response and creating a marker at each point to show the elevation information.

1. Extract the z values from the service response to be used for displaying the elevation at each point.

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       async function fetchElevationData() {
   
         const data = await arcgisRest.findElevationAtManyPoints({
           coordinates: points,
           authentication: arcgisRest.ApiKeyManager.fromKey(accessToken)
         });
   
         const elevationValues = data.result.points;
   
       }
   

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2. Use Popup to show a popup on top of each marker with the elevation value.

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       async function fetchElevationData() {
   
         const data = await arcgisRest.findElevationAtManyPoints({
           coordinates: points,
           authentication: arcgisRest.ApiKeyManager.fromKey(accessToken)
         });
   
         const elevationValues = data.result.points;
   
         elevationValues.forEach((elevationData) => {
           const { x, y, z } = elevationData;
           new maplibregl.Popup({ closeButton: false })
             .setLngLat([x, y])
             .setHTML(`${z} m`)
             .setOffset(40)
             .addTo(map);
         });
   
       }
   

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Run the app

Run the app.

You should now see a map centered over New Zealand's South Island with elevation values shown along the path.

What's next?

Learn how to use additional location services in these tutorials: