Buzzfeed's "Pound" re-implementation.
BuzzFeed Unveils Pound To Show How You Really Share Content | Fast Company | Business + Innovation
It automatically appends a hash named "footprint". For example, if you directly land to a page, you will get a hash something like ex8ceta4.
And then you might share the page via Twitter. The shared url will have the hash #ex8ceta4.
When someone clicks the link, they gets another footprint something like ex8ceta4+g4zawkjh. Note that your footprint ex8ceta4 is contained. Ok. Let them shared the page. The shared url has the hash #ex8ceta4+g4zawkjh.
Then next? It will be like ex8ceta4+g4zawkjh+ppae6owm. Simply a random string will be appended.
With this mechanism (and some referrer tracking), you can draw actual social spreading graph as below.
You can assume that footprint with one id (such as ex8ceta4) as directly landed users. A footprint with two id (such as ex8ceta4+g4zawkjh) as indirectly landed users, who comes from the sharing of the directly landed user. (ex8ceta4)
