There's a great guide on creating Custom Overlays for iOS MapKit at: http://shawnsbits.com/blog/2010/12/23/mapkit-overlays-session-1-overlay-map/
However it glosses over the part whereby you have to install Gdal. If your fairly new to Mac OS X and more familiar with a Windows background then you may need some extra info on how to go about it:
Download and install the Macports.dmg from http://www.macports.org/install.php
Once installed you will need to provide yourself root privilages if you dont have so already.
- Start System Preferences and select "Accounts".
- Under the list of users press the "Login Options", and then next to that press the "Join..." button next to Network Account Server. (You will not be joining a network account server, this is just the way to get to the Directory Utility).
- Press the button to "Open Directory Utility..."
- Once you launch the Directory Utility, however you do it, then enable the root account by doing the following:
- Click on the Lock icon and give the Administrator password to authenticate.
- Pull down the "Edit" menu to "Enable Root User"
- Pull down the "Edit" menu to "Change Root Password..." and enter a good, strong password for the root user.
Once you have root enabled you will need to go load up terminal (Applications - Utilites - Terminal)
Then simply enter "sudo port install gdal"
If all goes well Macports should begin downloading and installing the most upto date version of Gdal.