We’ve talked here before about [TileMill](http://www.pbs.org/idealab/2010/08/tilemill-custom-maps-to-help-with-data-dumps-hyper-local215.html), an open source tool for creating your own custom map tiles (the individual pieces that make up a full map of a city, country, and so on). But what sorts of things can you do with these map tiles? One area we wanted to explore was using them on Apple’s latest touch-based device, the iPad. Providing a touch interface for maps is a serious usability win and the long battery life, huge available storage, and opportunistic network connectivity combine to make a really attractive mobile mapping platform.
The result? The [MapBox iPad app](http://mapbox.com/ipad). This app allows you to use custom maps on the iPad (and in an [open format](http://mapbox.com/documentation/mbtiles-file-format)), as well as use [OpenStreetMap](http://www.openstreetmap.org/) (OSM) map tiles, overlay custom data in Google Earth’s popular KML format as well as GeoRSS, save and share map snapshots, and much more.
To create the app the first thing we had to figure out was an alternative to Apple’s standard MapKit toolset, which only uses online Google Maps. This was accomplished with the open source [route-me](https://github.com/route-me/route-me) library. Once this was decided, we created a file format called [MBTiles](http://developmentseed.org/blog/2010/oct/08/portable-map-tiles-format-released) to easily exchange potentially millions of tile images so they could be used offline.
We then layered on data visualizations, creating an open source library called [Simple KML](https://github.com/incanus/Simple-KML/) in order to parse and display the KML and KMZ file formats, something that hasn’t really been done much on the iPhone or iPad outside of Google’s own app.
To round out the initial release, we added the ability to save the current view — coordinates, zoom level, and data overlays — as a document for later, as well as the ability to email a picture of the current map straight from the app.
As a whole, we’ve been really happy with the iPad as an open mapping platform. We’ve used some tools, made some new ones available, and combined them all in new ways.
Do you have any ideas for open mapping on the iPad? We’d love to hear your thoughts in the comments or on Twitter, where you can follow our progress at [@MapBox](http://twitter.com/mapbox).