Edit

Sea Level


Go to San Francisco, New York, Mumbai, or Shanghai

Render sea level at different elevations

This example uses a ol/source/Raster with Mapbox Terrain-RGB tiles to "flood" areas below the elevation shown on the sea level slider.

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index.html<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Sea Level</title>
    <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
      #level {
        display: inline-block;
        width: 150px;
        vertical-align: text-bottom;
      }

      a.location {
        cursor: pointer;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <label>
      Sea level
      <input id="level" type="range" min="0" max="100" value="1"/>
      +<span id="output"></span> m
    </label>
    <br>
    Go to
    <a class="location" data-center="-122.3267,37.8377" data-zoom="11">San Francisco</a>,
    <a class="location" data-center="-73.9338,40.6861" data-zoom="11">New York</a>,
    <a class="location" data-center="72.9481,18.9929" data-zoom="11">Mumbai</a>, or
    <a class="location" data-center="120.831,31.160" data-zoom="9">Shanghai</a>
    <script src="index.js"></script>
  </body>
</html>
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index.jsimport 'ol/ol.css';
import Map from 'ol/Map';
import View from 'ol/View';
import {Image as ImageLayer, Tile as TileLayer} from 'ol/layer';
import {fromLonLat} from 'ol/proj';
import {Raster as RasterSource, TileJSON} from 'ol/source';
import XYZ from 'ol/source/XYZ';

function flood(pixels, data) {
  var pixel = pixels[0];
  if (pixel[3]) {
    var height = -10000 + ((pixel[0] * 256 * 256 + pixel[1] * 256 + pixel[2]) * 0.1);
    if (height <= data.level) {
      pixel[0] = 145;
      pixel[1] = 175;
      pixel[2] = 186;
      pixel[3] = 255;
    } else {
      pixel[3] = 0;
    }
  }
  return pixel;
}

var key = 'Your Mapbox access token from https://mapbox.com/ here';
var elevation = new XYZ({
  url: 'https://api.mapbox.com/v4/mapbox.terrain-rgb/{z}/{x}/{y}.pngraw?access_token=' + key,
  crossOrigin: 'anonymous'
});

var raster = new RasterSource({
  sources: [elevation],
  operation: flood
});

var map = new Map({
  target: 'map',
  layers: [
    new TileLayer({
      source: new TileJSON({
        url: 'https://api.tiles.mapbox.com/v4/mapbox.world-light.json?secure&access_token=' + key,
        crossOrigin: 'anonymous'
      })
    }),
    new ImageLayer({
      opacity: 0.6,
      source: raster
    })
  ],
  view: new View({
    center: fromLonLat([-122.3267, 37.8377]),
    zoom: 11
  })
});

var control = document.getElementById('level');
var output = document.getElementById('output');
control.addEventListener('input', function() {
  output.innerText = control.value;
  raster.changed();
});
output.innerText = control.value;

raster.on('beforeoperations', function(event) {
  event.data.level = control.value;
});

var locations = document.getElementsByClassName('location');
for (var i = 0, ii = locations.length; i < ii; ++i) {
  locations[i].addEventListener('click', relocate);
}

function relocate(event) {
  var data = event.target.dataset;
  var view = map.getView();
  view.setCenter(fromLonLat(data.center.split(',').map(Number)));
  view.setZoom(Number(data.zoom));
}
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package.json{
  "name": "sea-level",
  "dependencies": {
    "ol": "6.1.1"
  },
  "devDependencies": {
    "parcel": "1.11.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --experimental-scope-hoisting --public-url . index.html"
  }
}