Google Maps JavaScript API v3

Elevation Service

  1. Overview
  2. Elevation Requests
    1. Location Elevation Requests
    2. Path Elevation Requests
  3. Elevation Responses
    1. Elevation Status
    2. Elevation Results
  4. Elevation Examples

Overview

The Elevation service provides elevation data for locations on the surface of the earth, including depth locations on the ocean floor (which return negative values). In those cases where Google does not possess exact elevation measurements at the precise location you request, the service will interpolate and return an averaged value using the four nearest locations.

The ElevationService object provides you with a simple interface to query locations on the earth for elevation data. Additionally, you may request sampled elevation data along paths, allowing you to calculate the equidistant elevation changes along routes. The ElevationService object communicates with the Google Maps API Elevation Service which receives elevation requests and returns elevation data.

Note that these requests are rate-limited to discourage abuse of the service. If instead you wish to calculate elevations for static, known locations, see the Elevation Web Service documentation.

With the Elevation service, you can develop hiking and biking applications, mobile positioning applications, or low resolution surveying applications.

Elevation Requests

Accessing the Elevation service is asynchronous, since the Google Maps API needs to make a call to an external server. For that reason, you need to pass a callback method to execute upon completion of the request. This callback method should process the result(s). Note that the Elevation service returns a status code (ElevationStatus) and an array of separate ElevationResult objects.

The ElevationService handles two types of requests:

  • Requests for separate, discrete locations using the getElevationForLocations() method, which is passed a list of one or more locations using a LocationElevationRequest object.
  • Requests for elevation on a series of connected points along a path using the getElevationAlongPath() method, which is passed an ordered set of path vertices within a PathElevationRequest object. When requesting elevations along paths, you must also pass a parameter indicating how many samples you wish to take along that path.

Each of these methods must also pass a callback method to handle the returned ElevationResult and ElevationStatus objects.

Location Elevation Requests

A LocationElevationRequest object literal contains the following field:

{
  locations[]: LatLng
}

locations (required) defines the location(s) on the earth from which to return elevation data. This parameter takes an array of LatLngs.

You may pass any number of multiple coordinates within an array, as long as you don't exceed the service quotas. Note that when passing multiple coordinates, the accuracy of any returned data may be of lower resolution than when requesting data for a single coordinate.

Sampled Path Elevation Requests

A PathElevationRequest object literal contains the following fields:

{
  path[]: LatLng,
  samples: Number
}

These fields are explained below:

  • path (required) defines a path on the earth for which to return elevation data. The path parameter defines a set of two or more ordered {latitude,longitude} pairs using an array of two or more LatLng objects.
  • samples (required) specifies the number of sample points along a path for which to return elevation data. The samples parameter divides the given path into an ordered set of equidistant points along the path.

As with positional requests, the path parameter specifies a set of latitude and longitude values. Unlike a positional request, however, the path specifies an ordered set of vertices. Rather than return elevation data at the vertices, path requests are sampled along the length of the path, where each sample is equidistant from each other (inclusive of the endpoints).

Elevation Responses

For each valid request, the Elevation service will return to the defined callback a set of ElevationResult objects along with an ElevationStatus object.

Elevation Statuses

Each elevation request returns an ElevationStatus code within its callback function. This status code will contain one of the following values:

  • OK indicating the service request was successful
  • INVALID_REQUEST indicating the service request was malformed
  • OVER_QUERY_LIMIT indicating that the requestor has exceeded quota
  • REQUEST_DENIED indicating the service did not complete the request, likely because on an invalid parameter
  • UNKNOWN_ERROR indicating an unknown error

You should check that your callback succeeded by examining this status code for google.maps.ElevationStatus.OK.

Elevation Results

Upon success, the results argument of your callback function will contain a set of ElevationResult objects. These objects contain the following elements:

  • A location element (containing LatLng objects) of the position for which elevation data is being computed. Note that for path requests, the set of location elements will contain the sampled points along the path.
  • An elevation element indicating the elevation of the location in meters.
  • A resolution value, indicating the maximum distance between data points from which the elevation was interpolated, in meters. This property will be missing if the resolution is not known. Note that elevation data becomes more coarse (larger resolution values) when multiple points are passed. To obtain the most accurate elevation value for a point, it should be queried independently.

Elevation Examples

The following code translates a click on a map into an elevation request using the LocationElevationRequest object:

var elevator;
var map;
var infowindow = new google.maps.InfoWindow();
var denali = new google.maps.LatLng(63.3333333, -150.5);

function initialize() {
  var mapOptions = {
    zoom: 8,
    center: denali,
    mapTypeId: 'terrain'
  }
  map = new google.maps.Map(document.getElementById("map-canvas"), mapOptions);

  // Create an ElevationService
  elevator = new google.maps.ElevationService();

  // Add a listener for the click event and call getElevation on that location
  google.maps.event.addListener(map, 'click', getElevation);
}

function getElevation(event) {

  var locations = [];

  // Retrieve the clicked location and push it on the array
  var clickedLocation = event.latLng;
  locations.push(clickedLocation);

  // Create a LocationElevationRequest object using the array's one value
  var positionalRequest = {
    'locations': locations
  }

  // Initiate the location request
  elevator.getElevationForLocations(positionalRequest, function(results, status) {
    if (status == google.maps.ElevationStatus.OK) {

      // Retrieve the first result
      if (results[0]) {

        // Open an info window indicating the elevation at the clicked position
        infowindow.setContent("The elevation at this point 
is " + results[0].elevation + " meters."); infowindow.setPosition(clickedLocation); infowindow.open(map); } else { alert("No results found"); } } else { alert("Elevation service failed due to: " + status); } }); }

View example (elevation-simple.html)

The following example constructs a polyline given a set of coordinates and displays elevation data along that path using the Google Visualization API. (You must load this API using the Google Common Loader.) An elevation request is constructed using the PathElevationRequest:

var elevator;
var map;
var chart;
var infowindow = new google.maps.InfoWindow();
var polyline;

// The following path marks a general path from Mt.
// Whitney, the highest point in the continental United
// States to Badwater, Death Vallet, the lowest point.
var whitney = new google.maps.LatLng(36.578581, -118.291994);
var lonepine = new google.maps.LatLng(36.606111, -118.062778);
var owenslake = new google.maps.LatLng(36.433269, -117.950916);
var beattyjunction = new google.maps.LatLng(36.588056, -116.943056);
var panamintsprings = new google.maps.LatLng(36.339722, -117.467778);
var badwater = new google.maps.LatLng(36.23998, -116.83171);

// Load the Visualization API and the columnchart package.
google.load("visualization", "1", {packages: ["columnchart"]});

function initialize() {
  var mapOptions = {
    zoom: 8,
    center: lonepine,
    mapTypeId: 'terrain'
  }
  map = new google.maps.Map(document.getElementById("map-canvas"), mapOptions);

  // Create an ElevationService.
  elevator = new google.maps.ElevationService();

  // Draw the path, using the Visualization API and the Elevation service.
  drawPath();
}

function drawPath() {

  // Create a new chart in the elevation_chart DIV.
  chart = new google.visualization.ColumnChart(document.getElementById('elevation_chart'));

  var path = [ whitney, lonepine, owenslake, panamintsprings, beattyjunction, badwater];

  // Create a PathElevationRequest object using this array.
  // Ask for 256 samples along that path.
  var pathRequest = {
    'path': path,
    'samples': 256
  }

  // Initiate the path request.
  elevator.getElevationAlongPath(pathRequest, plotElevation);
}

// Takes an array of ElevationResult objects, draws the path on the map
// and plots the elevation profile on a Visualization API ColumnChart.
function plotElevation(results, status) {
  if (status == google.maps.ElevationStatus.OK) {
    elevations = results;

    // Extract the elevation samples from the returned results
    // and store them in an array of LatLngs.
    var elevationPath = [];
    for (var i = 0; i < results.length; i++) {
      elevationPath.push(elevations[i].location);
    }

    // Display a polyline of the elevation path.
    var pathOptions = {
      path: elevationPath,
      strokeColor: '#0000CC',
      opacity: 0.4,
      map: map
    }
    polyline = new google.maps.Polyline(pathOptions);

    // Extract the data from which to populate the chart.
    // Because the samples are equidistant, the 'Sample'
    // column here does double duty as distance along the
    // X axis.
    var data = new google.visualization.DataTable();
    data.addColumn('string', 'Sample');
    data.addColumn('number', 'Elevation');
    for (var i = 0; i < results.length; i++) {
      data.addRow(['', elevations[i].elevation]);
    }

    // Draw the chart using the data within its DIV.
    document.getElementById('elevation_chart').style.display = 'block';
    chart.draw(data, {
      width: 640,
      height: 200,
      legend: 'none',
      titleY: 'Elevation (m)'
    });
  }
}

View example (elevation-paths.html)

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