Google Map Maker in Pakistan

The month of June proved fruitful for mapping enthusiasts, tech buffs, and entrepreneurs throughout Pakistan as they gathered for a series of Google MapUps organized at universities in three major cities: Islamabad, Lahore and Karachi.

Led by Google Pakistan Country Consultant, Badar Khushnood and a trio of Pakistan’s Map Maker Advocates—Faraz Ahmad, Jabran Rafique and Omer Sheikh—the three events welcomed a total of 150 participants to learn the ins and outs of Google Map Maker. The intent of the MapUps was to guide new users through the process of mapping their cities and neighborhoods while stressing the importance of having a complete map of Pakistan available online.
Recent mapping efforts in Pakistan have been predominantly aligned with relief efforts following Pakistan’s 2010 floods and landslides, as demonstrated by Omer, Jabran and Faraz. Dr. Sayeed Ghani spoke at the Karachi MapUp about Sindh Flood Maps, his community-based geographic information system (GIS) that implements a Google Maps API to assist in disaster management. Dr. Sohaib Khan, who co-hosted the Lahore MapUp, has also focused on flood relief.

On a basic level, the aim of MapUps is to teach new and aspiring mappers the fundamentals of Map Maker, and to bring them together to map their community. Omer explained that “The idea is to get the participants started in the hope that they will continue mapping in the future.” Badar Khushnood and our Mapping Advocates ultimately highlighted the tools and motivation behind mapping, highlighting it as influential, inspirational, and humanitarian.

Google MapUp, NU-FAST, Islamabad, Pakistan
Learn more about hosting a Google MapUp in your own community, and be sure to visit our Advocates and other passionate and helpful mappers in our Map Your World Community.

How to Convert Tile Coordinates

In addition to referencing tiles by quadkey, Bing Maps also refers to tiles by x, y, and z coordinates. This is the way you reference tiles when overriding the GetUri() method of the Silverlight Microsoft.Maps.MapControl.TileSource class, for example, and the x, y, z properties of a tile are passed to the uriConstructor function specified in the options for an AJAX v7 Microsoft.Maps.TileSource.

In the x, y, z tile identification system:

  • z is the zoom level of the grid
  • x and y are the column and row number at which this tile should be placed, measured from an origin at the top left of the map.

Thus, at zoom level 1, you can describe the four tiles required to make a complete Bing Map using x, y, z coordinates as follows:


Bing Maps is not entirely unusual in this respect – this exact same referencing system is used by Google Maps, Open Street Maps, ESRI, and many others. You’d therefore be forgiven for thinking that it was some sort of standard.

In fact, this tile numbering sounds a lot like (and is often incorrectly described as) a  TMS index. The Tile Map Service (TMS) Specification defined by the Open Source Geospatial Foundation is a standard for serving map tiles that, like the system described above, places tiles on a grid and refers to their position using x, y, and z coordinates, where z is the zoom level, and x and y refer to column and row positions. However, according to the TMS specifications, “The x-coordinate of the tile numbers increases with the x-coordinate of the spatial reference system, and the y-coordinate of the tile numbers also increases with the y-coordinate of the spatial reference system.”. In other words, tile (0, 0), at any zoom level should always be placed at the bottom left of the map, not the top left.

Using the TMS system, the tile indexes at zoom level 1 become as follows:


The problem is that, since these systems are identical in almost every other respect, people tend to assume that the system used by Google/Bing/OSM et al. is the standard and systems that output tiles using it sometimes mistakenly refer to it as the TMS format. Then,  every now and again, you come across a piece of software or service that genuinely outputs tiles numbered according to the TMS standard and, if you don’t correct the tile origin, your tiles all end upside-down on the wrong side of the world :(

Fortunately, it’s a very simple correction to make. At any given map zoom level, zoom, you can invert the y index of a tile from TMS to Google/Bing as follows:

var ymax = 1 << zoom;
var y = ymax – y – 1;


Assuming that you have a set of TMS tiles stored in a subdirectory structure that follows the pattern /z/y/x.png (as described in the Tile Resources section of the OSGeo TMS standard), then here’s a full example showing how to add a tilelayer of TMS tiles to Bing Maps v7:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "">
<html xmlns="">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script type="text/javascript" src=""></script>
<script type="text/javascript">
var map = null;
function GetMap() {
// Create a basic map
map = new Microsoft.Maps.Map(document.getElementById("mapDiv"),
center: new Microsoft.Maps.Location(52.6, 1.26),
zoom: 12

// Create the tile source
var tileSource = new Microsoft.Maps.TileSource({ uriConstructor: getTMSTilePath });

// Construct the layer using the tile source
var tilelayer = new Microsoft.Maps.TileLayer({ mercator: tileSource, opacity: 1 });

// Push the tile layer to the map

function getTMSTilePath(tile) {

var x = tile.x;
var z = tile.levelOfDetail;
// Invert tile y origin from top to bottom of map
var ymax = 1 << z;
var y = ymax – tile.y – 1;

return location.href.substring(0, location.href.lastIndexOf(‘/’)) + "/" + z + "/" + x + "/" + y + ".png";
<body onload="GetMap();">
<div id=’mapDiv’ style="position:relative; width:1024px; height:768px;"></div>


As a final note, just to add to the confusion, the Web Map Tile Service (WMTS) recently published by the OGC provides an alternative standard to TMS, but, like Google/Bing, uses an origin at the top-left hand corner.

About Browsers and the Web

Late last year, Google released an illustrated online guidebook for everyday users who are curious about how browsers and the web work. In building 20 Things I Learned about Browsers and the Web with HTML5, JavaScript and CSS with our friends at Fi, we heard from many of you that you’d like to get your hands on the source code. Today, They’re open sourcing all the code for this web book at, so that you can use and tinker with the code for your own projects.

20 Things I Learned was celebrated this year as an Official Honoree at the 15th Annual Webby Awards in the categories of Education, Best Visual Design (Function), and Best Practices. For those of you who missed our initial release last year, here’s a quick recap of the APIs behind some of the web book’s popular features:

  • The book uses the HTML5 canvas element to animate some of the illustrations in the book and enhance the experience with transitions between the hard cover and soft pages of the book. The page flips, including all shadows and highlights, are generated procedurally through JavaScript and drawn on canvas. You can read more about the page flips on this HTML5rocks tutorial.
  • The book takes advantage of the Application Cache API so that is can be read offline after a user’s first visit.
  • With the Local Storage API, readers can resume reading where they left off.
  • The History API provides a clutter-free URL structure that can be indexed by search engines.
  • CSS3 features such as web fonts, animations, gradients and shadows are used to enhance the visual appeal of the app.

With this open source release, we’ve also taken the opportunity to translate 20 Things I Learned into 15 languages: Bahasa Indonesia, Brazilian Portuguese, Chinese (Simplified and Traditional), Czech, Dutch, English, French, German, Italian, Japanese, Polish, Russian, Spanish, and Tagalog.

We hope that web books like 20 Things I Learned continue to inspire web developers to find compelling ways to bring the power of open web technologies to education. 20 Things I Learned is best experienced in Chrome or any up-to-date, HTML5-compliant modern browser. For those of you who’ve previously read this web book, don’t forget to hit refresh on your browser to see the new language options.