Given enough data, this can be done automatically. A simple way to do it self-organizing maps (SOMs). On the top of this wiki page: http://en.wikipedia.org/wiki/Self-organizing_map there is an example where members of congress are grouped based on voting patterns.
Superficially it might seem that the SOM has created a left-right spectrum of sorts. Actually this is not the case, as the clustering distances show. Instead, what has been done is just that members have been grouped on a 2-d plane such that members with similar views are closer to each other.
This is a great article at Aeon magazine. The author argues that the new ideological dichotomy is going to be between people who have great faith in technology and human innovation (Up) and the people who believe that humans are much more tied to their biology and the Earth (Down).
LW of course is a very Up community.