How are weekly rankings determined?

Just a few rankings questions:
 
At what point does a forum show up on the rankings, for example, when a forum is in the top 2000?
 
What determines a visit?  Is this member visits, non-member visits, admin visits?
 
I am glad Lefora has a ranking system, because it lets me know how well my forum is doing. 
 
Thank you.

Any person will be considered a visitor (member or non member).

New forums may take a little while to show up in the rankings.  Private forums are not displayed in the rankings.