Google Latitude finally lands on the iPhone

Previously only available as a Web client in Safari, Google Latitude now has an app

And you thought Facebook Places was late to the game.

Google Latitude, Google’s location-sharing app, launched Monday on the iPhone, letting users automatically reveal their location to their other friends 24/7.

The app arrives almost a year and a half after Latitude launched on iPhone (via a Web client) and two months after Google created a dedicated website for the service. More importantly, however, Latitude drops on the iPhone a week after Foursquare announced that it had topped five million users.

While Google says nine million people already use Latitude for Android, BlackBerry, Symbian, and Windows Mobile smartphones, there’s no telling how active these users are (we’ve contacted Google for details but have not yet received response). If all or most of the nine million use the app default, which is to automatically update their location from the phone as they move about the world, then that’s pretty impressive. But if that’s just the number of times the app has been downloaded, then it’s not as striking.

On the other hand, five million users checking in to restaurants and bars from an app largely unknown in the public sphere, like Foursquare? Now that’s an accomplishment.

Here’s a screenshot from Google of what the app looks like when you have lots of nearby friends who use the app:

The only problem:

That’s a screenshot of the app on my phone, after downloading it from the App Store and accepting the terms & conditions. Where are my nine million friends?

I can pull down the “list” to refresh my friends’ locations, except it won’t do anything because, as you can probably tell, I currently don’t have any friends that use Latitude. Maybe I’m wrong, but this is how the app will look to a lot of people who try the app for the first time.

So what’s next? Well, in the upper righthand corner there are two buttons.

Clicking the little gears icon, users can configure settings directly from the app, like how Latitude reports location. The default is to simply detect the user’s location and automatically update accordingly. Another option lets the user manually select his or her location on the map and a third option, kind of defeating the whole point of the app, hides the user’s location from friends.

The other button will probably be a lot more useful to users, allowing you to invite friends to Latitude either by manually entering an email or by selecting iPhone or Google contacts. Google will also suggest friends for you, starting with Gmail contacts that actually use Latitude. I have three, but they’re not really friends of mine, so I’d feel weird asking them to let me see their every location.

Location networks, like social networks, know this problem all too well. How do you build up a foundation of users for an app whose sole benefit is the sharing of information with friends? If there are no friends, there is no app. Foursquare and other location apps like Gowalla manage to skirt this problem by offering game-like activities and rewards programs.

Now that Latitude has an iPhone app proper, though, it will be interesting to see how it fares in the location wars.