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Comment by klausa | Hacker News Reader

How is this techically possible? I was under impression that foursquare doesn't share your full public profile (including your twitter and/or facebook) when you show up in 'x is also here:'. I get it how it can look up girls that are nearby (scan for nearby 4sq venues, than if there are people in them, filter for girls...), but how can it link back to Facebook (unless you're friends with that person on 4sq and/or facebook, which makes whole point of this app moot)?

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I found it surprising too, but your impression is wrong.

When you query the Foursquare API for a user, Foursquare returns the user's Facebook and Twitter names in their response (if the user has provided them to Foursquare):

https://developer.foursquare.com/docs/responses/user (see the "contact" field)

Once you have that, you just query Facebook and Twitter for their publicly available profile, photos, likes, tweets, etc.

That would explain it, thanks.

It seems it actually links to your facebook/twitter from your profile page, at least it does on webapp, I'm not sure how it is on mobile.

I think that's wrong default and should be changed.

The Foursquare API explorer is the best demo of an API I have ever seen: https://developer.foursquare.com/docs/explore

Given 2 public social graphs (FB and 4sq), I'm sure it is not hard of an exercise to cross reference that information. It really is more of a data-mapping exercise using 2 APIs.

That's why freely adding lots of personal information is a bad idea.

Much as there are tools like 1Password for passwords, I think there should be like tools for usernames/emails.

This would then return some control back to the user.

But how would you cross reference it? From my usage of 4sq (which is limited, I only installed it maybe week ago.), when you check in to venue, and someone else is already there, you get "There are 3 persons already there!", with their avatars. You can tap on those avatars, and see some more info (John D., maybe some bio? I'm not sure, I do know that it doesn't give you their full name.), but I don't think that would be enough to cross match those. That's why I'm curious.

Well, that's part of their secret sauce right? =)

Off the top of my head, I'd say go look at the APIs for both FB and 4sq (try say user, friends, checkins, mayorship and location) and look at what is available for user PII and friends. Compare say username and do a little fuzzy matching on friend's names.

If say FB and 4sq share say more than x common friends, chances are you have the right mapping and you can build from that. Thrown in a Bayesian filter and pretty soon you will have a good model built up. Think of the 2 APIs as two sheets of paper with directed graphs on them. If you overlay them, the mapping becomes clear pretty quickly.

"Much as there are tools like 1Password for passwords, I think there should be like tools for usernames/emails."

The way I read that is an aggregator for usernames. How would that help anything?

Or do you mean I change my username to a different sha1 string for each website? That seems like it would definitely hurt the social aspect of a lot of websites...

"2fd4e1c67a2d28fced849ee1bb76e7391b93eb12 just checked in at Alice and Bob's Bar"

I was thinking more along the lines of having unique emails per site. While usernames have a higher probability of being the same person across different sites, it's not guaranteed. twitter.com/ed may not be facebook.com/ed but foo@bar.com is definitely unique.

The goal would be to make email one less piece of PII to aggregate you across sites as well as helping narrow down who is selling your info. I am well aware of the <username>+foo convention of gmail but it is trival to strip off the +foo part.

This way, you still get mail that you want without having to give out your "real" email address.

Maybe it's wasted effort but personally, I think there is some value there (for the people that care).

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