I frequently get a sense of deja vu when I see pictures of cities in ST episodes such as this one:- I get the impression that many of the sets are used over and over for different stories set on different planets. Has anyone ever done a comparative study on this?
I think most matte paintings in TOS were used twice. EDIT: Yup, from another page of the above article: http://www.ex-astris-scientia.org/inconsistencies/tos_surfaces.htm