Parallel Kingdom is a location-based game that lays a massively multiplayer online role-playing game over the top of a Google map of your current surroundings. It’s not the only game of its kind, but it’s a very cool concept, one that points toward the future for much of mobile gaming — and for the mobile incarnation of social media as well. Think of location-based gaming as the teaspoon of sugar that’s going to help people swallow location-based services in general.

PK is fairly straightforward, giving you simple mobs to hunt down and resources to collect, within half a mile of your GPS-determined or tower-triangulated location, whether you’re on an iPhone or an Android handset. One note: I got the game going on my iPhone for about a day, but haven’t been able to get it launched since. According to a recent interview with the developers, however, there are about 70,000 more or less active players, which sounds fairly respectable to me, given the nature of the game.

Things get interesting when you notice that PK shows you the location of other players near you, and lets you interact with them, either in duels or by grouping up to go adventuring together. There are few ways to venture far outside your current location on the map without physically getting up and moving, but your contacts can invite you to join them at their real-life location, which is a nice touch. You seem to be able to plant a flag when you’re across town, then visit it from your home location, and you can stake a claim to real-life plots of land, which is interesting. A new version of the game (no longer free), is apparently due out very shortly.

Games like Parallel Kingdom are important, for a couple of reasons. (Here’s Wikipedia’s somewhat random list of location-based games. I’ve also been checking out Sphericle, which seems to have at least a small community of players.) Expect to see more of these kinds of games qua games, as powerful mobile devices become more widespread and people and become more accustomed to having information streamed to them on the go.

But location-based games are also going to be part of what gets people used to location-based services in general. Apps like Foursquare are already using game mechanics get people engaged, giving users points for “checking in” at the establishments they frequent. These and others are already giving us a taste of what life may be like when we’re streaming our locations to our friends all the time.

One thing that’s interesting to note is that this could well mean a return to the time when relationships with the people you actually knew and saw every day had a different status than those you just kept up with online. Needless to say, we never really left that time, but when you’re Facebook “friends” both with your significant other and with people you’ve never physically met, it begins to feel that way. Will we soon have Facebook “acquaintances” as well as friends? You can create cohorts using the broadcast and privacy tools of a service like Facebook, of course, but when those services start to offer such labels explicitly, you’ll know we’ve moved on to the next stage of their evolution.