XKCD updated his famous Online Communities map (the first one was released in 2007). Tumblr appears North of the Photoblogs island, in the Sea of Opinions. About this map:

Communities rise and fall, and total membership numbers are no longer a good measure of a community’s current size and health. This updated map uses size to represent total social activity in a community ― that is, how much talking, playing, sharing, or other socializing happens there. This meant some comparing of apples and oranges, but I did my best and tried to be consistent.

Estimates are based on the best numbers I could find, but involved a great deal of guesswork, statistical inference, random sampling, nonrandom sampling, a 20,000-cell spreadsheet, emailing, cajoling, tea-leaf reading, goat sacrifices, and gut instinct (i.e. making things up).

Sources of data include Google and Bing, Wikipedia, Alexa, Big-Boards.com, StumbleUpon, Wordpress, Askimet, every website statistics page I could find, press releases, news articles, and individual site employees. Tanks in particular to folks at Last.fm, LiveJournal, Reddit, and The New York Times, as well as sysadmins at a number of sites who shared statistics on condition of anonymity.

Previously on Skandalon