Many parts of the world, where there is no access to Internet and it really becomes difficult for people navigating from one place to another without having mobile data or internet to get right directions. To overcome this situations Google takes a major steps to help people across globe find directions and get where they are going, even when they are out of mobile data or Internet access.
Now you can download an area of the world to your phone, and the next time you find there's no connectivity -- whether it's a country road or an underground parking garage -- Google Maps will continue to work seamlessly. Whereas before you could simply view an area of the map offline, now you can get turn-by-turn driving directions, search for specific destinations, and find useful information about places, like hours of operation, contact information or ratings.
You can download an area by searching for a city, county or country, for instance, and tapping "Download" on the resulting place sheet, or by going to "Offline Areas" in the Google Maps menu and tapping on the "+" button. Once downloaded, Google Maps will move into offline mode automatically when it recognizes you are in a location with spotty service or no connectivity at all. When a connection is found, it will switch back online so you can easily access the full version of Maps, including live traffic conditions for your current route. By default, Google'll only download areas to your device when are on a Wi-Fi connection to prevent large data fees.
As of now Google Maps is only available for Android Smartphones. It will be coming soon to iOS.
Source: Google Maps Blog