Toponymy is the taxonomic study of place names, their origins and their meanings. The word is derived from the Greek topos, place, and ounouma, name. It is itself a branch of onomastics, the study of names of all kinds.
For an example of Wikipedia work in this area see List of generic forms in British place names.
On a lighter note, see also: List of interesting or unusual place names
wikipedia.org dumped 2003-03-17 with terodump