one minute demo of metro extracts

<!DOCTYPE html>
<html>
  <head>
    <title>Layer selector example | CartoDB.js</title>
    <meta name="viewport" content="initial-scale=1.0, user-scalable=no" />
    <meta http-equiv="content-type" content="text/html; charset=UTF-8"/>
    <link rel="shortcut icon" href="https://cartodb.com/assets/favicon.ico" />
    <style>
      html, body, #map {
        height: 100%;
        padding: 0;
        margin: 0;
        background: black;
      }
    </style>
 
    <link rel="stylesheet" href="https://libs.cartocdn.com/cartodb.js/v3/themes/css/cartodb.css" />
    
  </head>
  <body>
    <div id="map"></div>

<script src="https://libs.cartocdn.com/cartodb.js/v3/cartodb.js"></script>
 
    <script>
      var map;
      function featureClick(e, pos, latlng, data){
        // var sql = new cartodb.SQL({ user: 'documentation' });
        console.log(data)
        if(map.getZoom() < 7){
          map.setView([data.lat,data.lng],7)
        } else {

var url = "https://osm.cartodb.com/api/v2/sql?format=shp&q=select the_geom,hstore_to_json(tags) as tags from osm_all WHERE the_geom %26%26 ST_SetSRID('"+data.bbox+"'::geometry, 4326)";
          window.location = url;
        }
      }
 
      function main() {

// get the currently selected style
        selectedStyle = $('li.selected').attr('id');
 
        cartodb.createVis('map','https://osm2.cartodb.com/api/v2/viz/cf26d670-009b-11e4-830e-0e73339ffa50/viz.json')
        .done(function(vis, layers) {
          // createSelector(layers);
          map = vis.getNativeMap();
          layer = layers[1].getSubLayer(0);
          layer.set({sql: 'SELECT cartodb_id, the_geom, area_sqkm, the_geom_webmercator, ST_ASText(the_geom) bbox, ST_X(ST_Centroid(the_geom)) lng, ST_Y(ST_Centroid(the_geom)) lat FROM ne_10m_urban_areas_bbox ORDER BY area_sqkm DESC',interactivity: 'cartodb_id, bbox, lat, lng'})
          layer.setInteraction(true);
          layer.on('featureClick', featureClick);
        })
        .error(function(err) {
          console.log(err);
        });
      }
 
      window.onload = main;
    </script>
  </body>
</html>

Modified http://libs.cartocdn.com/cartodb.js/v3/cartodb.js to a secure url

https://libs.cartocdn.com/cartodb.js/v3/cartodb.js