To sort a table by a certain column, click on the arrow next to the column title.
If you want to know which offices are using two different forms of social media, or if you want to know which members from a state are using a form of social media, you will need to sort twice, but in a particular order.
For example: If you wanted to know which offices use both Flickr and Twitter, or which offices use Flicker but not twitter, refresh the page and sort by Flickr and THEN sort by Twitter. This will cause the list to sort all the offices that use both forms first, followed by those that use Twitter only, followed by those that use Flickr only.
Another example: If you want to know which Democratic Congressmen from California use Twitter, first sort by district, then by party and then by Twitter. That sort tells me that 11 Democrats from the California delegation use twitter.
The general rule is to sort by the least common item (Flickr) first and the most common (Facebook) last.
For further information, see Wikipedia's sorting help section
If you have any questions, please don't hesitate to ask firstname.lastname@example.org