I used to live in LA County and when I had time to kill in my car I'd just sit and flip through the Thomas Guide and marvel at all the different communities, roads, etc., there were. Such a smorgasbord of big, small and in-between cities and towns.
I'd love to see you do one for other major counties like Riverside, San Bernardino, San Diego, Orange, etc. :-)
I grew up in Los Angeles, so the county has a special place in my heart.
With regard to the other counties – I feel as if Los Angeles County was suitable because of the density and how often, when driving on a motorway (freeway), one will see the various city names. I'm not so sure the inland counties would be as familiar, but I'll do some investigating!