City Maps 2Go, a popular offline map for iOS operating system based devices like iPod Touch, iPhone and iPad, is available for free for today. The App is otherwise costs $1.99 or Rs 100 approximately.
The map comes with lifetime free download, Wikipedia travel guide for world, and a guarantee to offer map of every place in the world. However Wikipedia travel guide is available for only one map for free, for all maps you need to pay some amount. The developers of the app claim that if there is a map missing for a place, it will be added immediately on request.
The offline maps do not need data connectivity post download and works with the inbuilt GPS of the device or with cell site information. This is different from cloud based mapping service like Google Map, which downloads the portion of the map from the server temporarily, for which you will need a data connection.