this is kewl, I must play this game in my city too!! :)-

This seems to me identical to GeoCaching

Splasho – you're right that what we're doing with the project may be thought of as a specific kind of GeoCaching. But GC uses a GPS device, which many people might be unwilling to invest in.

I see what you mean Dan, it's a nice idea.

Brillant!

It would be letterboxing then.