I'm in ur base, bein ur mayor.

The advance of civilization is nothing but an exercise in the limiting of privacy.
 - Isaac Asimov

What is foursquare for? I signed up the day after receiving my shiny new überphone, having heard that it was one of the must-have apps for any self-respecting technology nerd. Somewhat sheeplike, yes, but I went into this brave new world of smartphones and whizzy, often unstable software offerings determined to keep an open mind. If an app was cool, or useful, I'd keep it; if not, well, it would be simple enough to toss the thing back into the digital ether from whence it spawned.

For those tumbling arse over tit in the wake of the great frothing wave of technological innovation, foursquare is a location-based service which uses your fancy phone's GPS to track you, and encourages you to 'checkin' to any number of user-created locations as you pass through them during your day-to-day. It's a game, of sorts, in which you receive points based on the number and frequency of your checkins, and for discovering new places, and for sharing tips on the locations you visit. So you might recommend a certain dish at a restaurant, or point out something cool in your local park which people might overlook. You also receive badges, which are like achievements on Xbox Live and the like, for - well, all manner of things, from being a prolific checker-in (checkinnerer?) to visting far-flung places to becoming the mayor of certain numbers of locations...

Yes, mayorship - the other main achievement foursquare hands out. Whoever has checked in to a location the most is considered its mayor. With this post comes great responsibility, tireless work for the public good, and the respect of your peers (or backroom politics, brown envelopes full of deniable donations and a surfeit of succeptible interns, depending on personal preference and fictional genre).

Actually, with this post comes nothing. Maybe a badge, which is just another flavour of nothing. But it's all part of the game, and in the same way as Farmville and other tedious grinds can be interpreted as fun, so can this. You compete with your friends, try to get more badges or oust them as mayor of a closely-contested location, or simply share your thoughts and experiences of the world you inhabit with an Internet's-worth of strangers. It's a social networking site where the building blocks of interaction aren't mass uploads of holiday photos or pithy snapshots of daily life, but the places we go and the things we do there. It's building a picture of our world and layering it with information, recording our movements in something approaching real time and using that data to better understand the way society ticks.

The implications of which are juuust a little bit creepy, a point which was driven home last week when I checked into 'Home' to find I was no longer alone. I had, in fact, been ousted as mayor of my own home, and there was an intruder in my place. Absurd, isn't it, the amount of shock I felt at this? The sense of violation? The location I'd called 'Home' was nothing more than an arbitrary marker in a digital map. It didn't even correspond with the position of my 'real' house (once it occured to me, some three hours after creating the location, that perhaps advertising my home address and pinpointing it to within three square feet on Google Maps wasn't the wisest course).

But it was my home. I'd named it, staked out my claim to this particular patch of digital real estate. And more importantly, I'd invested in it emotionally. To find this private spot - which was, of course, publically available on an open website - so casually invaded was enough to make me want to quit foursquare without looking back. I changed the name of 'Home' to 'Foundry Lane' by a kind of reflex, an autonomous distancing mechanism, and didn't open foursquare again for several days.

Now I'm back on it, and engaged in a furious struggle with a complete stranger - who is, presumably, one of my neighbours - for mastery of Foundry Lane. If my digital home invader has done anything, he's made me consider the foursquare service and location tracking as a whole in a rather different light. Yes, a techno-savvy burglar might be able to plot my movements and ascertain the ideal moment to break in and ravage my prize collection of discarded beer bottles and fossilised spiders - but anyone could do that just by watching to see when I'd left the house, or hell, breaking in during the nine-to-five and trusting that probability'll swing in their favour.

The more troubling implications are inherent to the service itself. What I'm effectively doing is voluntarily submitting to intensive personal surveillance, where my movements and actions are recorded and held by an anonymous corporate agency. Of course this is nothing new; the amount of information Amazon.co.uk possesses regarding my shopping habits is doubtless enough to deforest a couple of square kilometres of eponymous rainforest, were it to be printed out. Likewise, I shudder to think of what Google can piece together about my personality, preferences and embarrassing pecadilloes, particularly since I signed up to iGoogle, effectively allowing all my searches to be more precisely collected and analysed - selling my digital soul for little more than a set of shiny bells 'n' whistles.

But there's still something a little... uncanny about foursquare, a troubling sensation that what you're doing is somehow in violation of the rules. Seaches and internet shopping don't have the same tangibility that your physical location does, that sense of unease that comes with someone watching you. I've yet to checkin at my workplace, despite at least one other foursquarer doing so and our head office address being clearly displayed on every page of the company website. Perhaps its paranoid, but I don't want somebody at foursquare to be so easily able to piece together every aspect of my daily life.

All the uproar regarding ID cards and the surrender of civil liberties, yet here we are submitting to a more genteel version of a home monitoring device. I'm effectively my own Big Brother.