What are the main sub-areas of theoretical computer science? I often want to give students a broad view of theoretical computer science, in the beginning of algorithms class or when advising a new student. It is hard for me to decide which sub-areas to talk about and how much emphasis to put on each of them. 

Therefore, my question is: What are the main sub-areas of theoretical computer science and what is their relative "size"? Let's say the size is the number of researchers who work mostly in that area.

Of course the division into sub-areas is a clustering problem with no unique answer. I also don't expect people to have precise statistics for the size of each area, but some feeling of the relative sizes is already helpful.
Also I wonder if 'size' is the right metric. that tends to vary as subfields come in and out of fashion. For example, a visitor from the 1980s would be very puzzled as to where all the parallel algorithms disappeared to. Someone attending SoCG in the last five years would think that we should call it the Symposium on Computational Topology :). 

Maybe the best thing to do is to let the student browse proceedings from theory conferences to get a sense of what's in vogue RIGHT NOW, and emphasize that this answer will change over time.