So the overwhelming problem for an augmented reality game is content creation, amirite? I mean, the real world is big. Way, way bigger than any virtual world I'm aware of. To reach a national or international audience, an augmented reality game can't rely on traditional video-game content creation pipelines. You need to either crowdsource content creation, restrict yourself to a small locality, or auto-generate content somehow. Or some combination.
So here's how I think you solve it, I'll put it in the familiar frame of an MMO, because I don't have a strong theme idea yet...
Your baseline game takes some huge local dataset like Yelp or whatevs, crunches it, and turns each node into a spawn point for critters based on the node. So a Chinese restaurant creates Chinese Food creeps that wander around the vicinity. You may or may not want to make a sophisticated thematic mapping algorithm so that all your creeps aren't ethnic food? I guess it depends on the game...
So anyway one dataset/layer gives you mobs for any populated area. Make your second layer something more explicit like the geocaching dataset. May as well include all this free content in your game, right? Caches become boss monsters or quests.
Next, give your players input into the game. As they do stuff they go up levels. The average level of players in the vicinity affects the average difficulty of the area. So if a bunch of high level bozos live in a town, then the newbs need to be careful when visiting, for example. Which means that your dedicated players will create your high level content. And the developer's office naturally becomes the highest level content in the game.
From there you might as well keep layering in every dataset you can think of, crime statistics, UPA pickup games, movie times, house prices, really anything.
What's the central activity of this game? Killing creeps? Collecting shiny stuff? Damned if I know. What kinds of things do people even do outside? What kind of augmented reality game would you like to play?