While Apple is getting ready to replace Google Maps with its own native mapping app on iOS, Google is beefing up its Google Earth app on the platform adding 3D maps and a handy tour guide feature. Owners of the new iPad, the iPad 2 and the iPhone 4S can now virtually fly through a growing list of cities including Boston, Los Angeles, San Diego, Santa Cruz, San Francisco and Rome in three dimensions on Google Earth.

“We’ll keep building and releasing 3D imagery for new locations as fast as we can and by the end of the year we aim to have coverage for metropolitan areas with a combined population of 300 million people,” said Peter Birch, Google Earth Product Manager in a post on Google’s Lat Long blog.

Google’s recently introduced tour guide feature is now available for iOS, enabling iDevice owners to discover and explore popular sites in more than 110 countries and regions.

“We’ve put together short tours of thousands of famous places and historical sites across the globe so it’s easier than ever to discover amazing places,” said Birch. “Just pull up the tab at the bottom of the screen to open the tour guide. Each image highlights a tours or place of interest in the area you are looking. Click on an item and you will be flown there. As you fly in and around the sites, snippets from Wikipedia provide additional information about the location. It’s like having a local expert right beside you!”

Google released a similar update to its Google Earth app for Android last month.