It's not just looking at e-mail contact lists. If you have entered other information in your profile (where you live, where you work, where you go/went to school, etc.), LinkedIn and Facebook look at those parameters and match them with other people who have the same data entered in those fields. It's basically one big fucking Data>Sort>Sort By>Column H>Column K>Column J>Column G>Column A for a huge-ass Excel spreadsheet.
It's more fun when you indicate you go to a large university/college, or work at some major, nationwide company.
For example, if you say you work at a nationwide retail chain, like Target, and only say "Target", it will look at all other people who say they also work at Target, even if it's not the same Target you work at. You could be working at the one in Conyers, Georgia, but even if you specified that you work at that specific Target location, the website's data-mining program will see "Target", and will suggest someone who works at a Target up in Tennessee, or over in Colorado, or Arizona, or New Mexico, or even up in North Dakota or Minnesota.
It could also be looking at the field or category Target falls under ("retail"), and end up suggesting people who work in the same or similar fields, and be employed at Wal-Mart, K-Mart, Sears, or perhaps something slightly more upscale, like Ross, Belk, Kohl's, or even some privately-owned small retail store found only in a handful of cities in a small area, like "Bobbie's Discount Boutique".
The point is, it looks at certain key words or phrases, and then like I said, does one big fucking Sort Data on a giant Excel spreadsheet.
I've had friends suggested for me on Facebook mainly due to there being x number of mutual friends between us, but I've also had people suggested because they either went or go to my old high school, lived or presently live in a city I used to live in, or live in now, or worked or presently work at a place I used to work at or work at now. Most of those that fall into either of those last two turn out to be younger than me. The "mutual friends" thing tends to be all over the map agewise.
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