Opacity control

Click and drag a slider to adjust the opacity of an overlay.

<!DOCTYPE html>
<html>
<head>
<meta charset=utf-8 />
<title>Opacity control</title>
<meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
<script src='https://api.mapbox.com/mapbox.js/v3.1.0/mapbox.js'></script>
<link href='https://api.mapbox.com/mapbox.js/v3.1.0/mapbox.css' rel='stylesheet' />
<style>
  body { margin:0; padding:0; }
  #map { position:absolute; top:0; bottom:0; width:100%; }
</style>
</head>
<body>
<style>
.ui-opacity {
  background:#FFF;
  position:absolute;
  left:10px;
  top:70px;
  height:200px;
  width:28px;
  border:1px solid rgba(0,0,0,0.4);
  border-radius:3px;
  z-index:1000;
  }
.ui-opacity .handle {
  position:absolute;
  background:#404040;
  left:0;
  top:20px;
  width:26px;
  height:10px;
  border-radius:1px;
  cursor:pointer;
  cursor:ns-resize;
  }
  .ui-opacity .handle:hover {
    background:#303030;
    }
</style>

<div id='map'></div>
<div id='control' class='ui-opacity'>
  <div id='handle' class='handle'></div>
</div>

<script>
L.mapbox.accessToken = '<your access token here>';
var handle = document.getElementById('handle'),
    start = false,
    startTop;

var map = L.mapbox.map('map', 'mapbox.emerald')
    .setView([43.6654, -79.4775], 14);

var overlay = L.mapbox.tileLayer('aibram.Aerial', {
      zIndex: 2
    })
    .addTo(map);

document.onmousemove = function(e) {
    if (!start) return;
    // Adjust control.
    handle.style.top = Math.max(-5, Math.min(195, startTop + parseInt(e.clientY, 10) - start)) + 'px';
    // Adjust opacity.
    overlay.setOpacity(1 - (handle.offsetTop / 200));
};

handle.onmousedown = function(e) {
    // Record initial positions.
    start = parseInt(e.clientY, 10);
    startTop = handle.offsetTop - 5;
    return false;
};

document.onmouseup = function(e) {
    start = null;
};
</script>
to create your own custom map and use it in this example.
Use this example by copying its source into your own HTML page and replacing the Map ID with one of your own from your projects. Having trouble with JavaScript? Try out Codecademy or contact our support team.
Copy example