Google knows a lot about its users. Facebook knows a lot about its users. FitBit knows a lot about its users. And so on.

But what happens when these companies all sell their data sets to one another? It'd be pretty trivial to link even anonymized users from set to set by looking for specific features. If I went for a run, Google tracked my location, FitBit tracked my heart rate, and Facebook tracked my status about my new best mile time, for example. Thus, Google can narrow down who I am in the other sets using pre-existing information that coincides with theirs. With enough overlap they can figure out exactly who I am fairly easily. Furthermore, each additional layer of data makes this discovery process from new data sets even easier, as it gives more opportunities to confirm or rule out concurrent info. So then when, say, Credit Karma, Comcast, and Amazon's data enter the fray, my online identity stops looking like an individual egg in each different basket but a whole lot of eggs in all in one. And they can do this across millions/billions of users--not just me!

I don't know for certain that this is a thing that happens, but... I have to assume it definitely is happening, right? How could it not? With how valuable data is and how loose protections are, this seems like a logical and potentially very lucrative step.

Right now, is there an aggregate version of "me" that exists in a data store somewhere that is a more comprehensive and accurate picture than my own self-image? After all, my memory and perception are imperfect and biased, but data stores aren't.