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Fly to a location based on scroll position

This example shows a map on the left and a scrollable story with several chapters on the right. A user can scroll through the story and the map will fly to the corresponding location for each chapter.

When the user scrolls, the application recognizes which chapter is on screen, and uses flyTo to animate the transition to that chapter's unique CameraOptions on the map.

<!DOCTYPE html>
<meta charset="utf-8">
<title>Fly to a location based on scroll position</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no">
<link href="" rel="stylesheet">
<script src=""></script>
body { margin: 0; padding: 0; }
#map { position: absolute; top: 0; bottom: 0; width: 100%; }
#map {
position: fixed;
width: 50%;
#features {
width: 50%;
margin-left: 50%;
font-family: sans-serif;
overflow-y: scroll;
background-color: #fafafa;
section {
padding: 25px 50px;
line-height: 25px;
border-bottom: 1px solid #ddd;
opacity: 0.25;
font-size: 13px;
} {
opacity: 1;
section:last-child {
border-bottom: none;
margin-bottom: 200px;

<div id="map"></div>
<div id="features">
<section id="baker" class="active">
<h3>221b Baker St.</h3>
November 1895. London is shrouded in fog and Sherlock Holmes and
Watson pass time restlessly awaiting a new case. "The London
criminal is certainly a dull fellow," Sherlock bemoans. "There have
been numerous petty thefts," Watson offers in response. Just then a
telegram arrives from Sherlock's brother Mycroft with a mysterious
<section id="aldgate">
<h3>Aldgate Station</h3>
Arthur Cadogan West was found dead, head crushed in on train tracks
at Aldgate Station at 6AM Tuesday morning. West worked at Woolwich
Arsenal on the Bruce-Partington submarine, a secret military
project. Plans for the submarine had been stolen and seven of the
ten missing papers were found in West's possession. Mycroft implores
Sherlock to take the case and recover the three missing papers.
<section id="london-bridge">
<h3>London Bridge</h3>
Holmes and Watson's investigations take them across London. Sherlock
deduces that West was murdered elsewhere, then moved to Aldgate
Station to create the illusion that he was crushed on the tracks by
a train. On their way to Woolwich Sherlock dispatches a telegram to
Mycroft at London Bridge: "Send list of all foreign spies known to
be in England, with full address."
<section id="woolwich">
<h3>Woolwich Arsenal</h3>
While investigating at Woolwich Arsenal Sherlock learns that West
did not have the three keys&mdash;door, office, and
safe&mdash;necessary to steal the papers. The train station clerk
mentions seeing an agitated West boarding the 8:15 train to London
Bridge. Sherlock suspects West of following someone who had access
to the Woolwich chief's keyring with all three keys.
<section id="gloucester">
<h3>Gloucester Road</h3>
Mycroft responds to Sherlock's telegram and mentions several spies.
Hugo Oberstein of 13 Caulfield Gardens catches Sherlock's eye. He
heads to the nearby Gloucester Road station to investigate and
learns that the windows of Caulfield Gardens open over rail tracks
where trains stop frequently.
<section id="caulfield-gardens">
<h3>13 Caulfield Gardens</h3>
Holmes deduces that the murderer placed West atop a stopped train at
Caulfield Gardens. The train traveled to Aldgate Station before
West's body finally toppled off. Backtracking to the criminal's
apartment, Holmes finds a series of classified ads from
<em>The Daily Telegraph</em> stashed away. All are under the name
Pierrot: "Monday night after nine. Two taps. Only ourselves. Do not
be so suspicious. Payment in hard cash when goods delivered."
<section id="telegraph">
<h3>The Daily Telegraph</h3>
Holmes and Watson head to The Daily Telegraph and place an ad to
draw out the criminal. It reads: "To-night. Same hour. Same place.
Two taps. Most vitally important. Your own safety at stake.
Pierrot." The trap works and Holmes catches the criminal: Colonel
Valentine Walter, the brother of Woolwich Arsenal's chief. He
confesses to working for Hugo Oberstein to obtain the submarine
plans in order to pay off his debts.
<section id="charing-cross">
<h3>Charing Cross Hotel</h3>
Walter writes to Oberstein and convinces him to meet in the smoking
room of the Charing Cross Hotel where he promises additional plans
for the submarine in exchange for money. The plan works and Holmes
and Watson catch both criminals.
<small id="citation">
Adapted from
<a href="">Project Gutenberg</a>
mapboxgl.accessToken = 'YOUR_MAPBOX_ACCESS_TOKEN';
const map = new mapboxgl.Map({
container: 'map',
// Choose from Mapbox's core styles, or make your own style with Mapbox Studio
style: 'mapbox://styles/mapbox/streets-v12',
center: [-0.15591514, 51.51830379],
zoom: 15.5,
bearing: 27,
pitch: 45

const chapters = {
'baker': {
bearing: 27,
center: [-0.15591514, 51.51830379],
zoom: 15.5,
pitch: 20
'aldgate': {
duration: 6000,
center: [-0.07571203, 51.51424049],
bearing: 150,
zoom: 15,
pitch: 0
'london-bridge': {
bearing: 90,
center: [-0.08533793, 51.50438536],
zoom: 13,
speed: 0.6,
pitch: 40
'woolwich': {
bearing: 90,
center: [0.05991101, 51.48752939],
zoom: 12.3
'gloucester': {
bearing: 45,
center: [-0.18335806, 51.49439521],
zoom: 15.3,
pitch: 20,
speed: 0.5
'caulfield-gardens': {
bearing: 180,
center: [-0.19684993, 51.5033856],
zoom: 12.3
'telegraph': {
bearing: 90,
center: [-0.10669358, 51.51433123],
zoom: 17.3,
pitch: 40
'charing-cross': {
bearing: 90,
center: [-0.12416858, 51.50779757],
zoom: 14.3,
pitch: 20

let activeChapterName = 'baker';
function setActiveChapter(chapterName) {
if (chapterName === activeChapterName) return;



activeChapterName = chapterName;

function isElementOnScreen(id) {
const element = document.getElementById(id);
const bounds = element.getBoundingClientRect();
return < window.innerHeight && bounds.bottom > 0;

// On every scroll event, check which element is on screen
window.onscroll = () => {
for (const chapterName in chapters) {
if (isElementOnScreen(chapterName)) {

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