In one of our favorite Valentine’s Day posts of all time, Chris Dixon posted about the “geo stack” – a model for how to think about the various layers of the geolocation ecosystem.  According to Chris, the stack looks something like this: lat long detection > lat long translation (into venues, addresses, etc.) > user relationship (how to get consumers to share location) > recommendations (tips, reviews, etc.) > social graphs > monetization.  If you haven’t already, please click through and read the whole post – the comments are worth reading as well.

We’ve taken the liberty of trying to visualize this stack with a few tweaks and notes – for instance, we’ve included social graph in the “User Relationship” layer, and example companies who we see as competing at the various layers:

If you are working on something in the geolocation / social check-in space, you may find it helpful to think about where you fit into this stack, and what you need to do to stake and defend your claim in what is rapidly becoming a very competitive area.

A new social check-in app called PlacePop quietly joined the social checkin space over the weekend.

This is what they have to offer so far:

PlacePop doesn’t seem to bring anything new to the table, but the features that are there are nicely designed.  The aggregation is especially well done (another social checkin company that is doing heavy aggregation is Buzzd).  To the untrained eye, this will look like an app with a lot of users.

Somehow, friending beyond one by one invites didn’t make it into the release version of the app.  I’m sure there was a heated internal discussion about that – while it’s great to get something out the door, not having Facebook and Twitter integrated friending for launch in a social app is an unusual move.

Via their URL structure, it looks like there are about 1585 different profiles set up for PlacePop so far.

Oh yeah, one final little tidbit about PlacePop – it was developed by Ooga Labs, and is headed by Kent Lindstrom, the ex President of Friendster who led that company’s turnaround.

Why is this important?  Because if you ran a high profile social network, you are, or know, a master in viral distribution.

And as PlacePop is late to the game and light on features, winning on distribution is just about their only chance.