Herman Overmars - I know surnames weren't common in the distant past and people were sometimes identified by place names, occupations or simply designations for son of or daughter of. My Dutch ancestors have not been traced to a specific place named Nieuwkirk in the Netherlands. I have them traced to the 1600's in what is now New York where they used van Nieuwkirk, or van Niewkirk as a surname before it became Newkirk. I have ancestors who used van Bunschoten (A few different spellings) who were indeed from Bunschoten, Utrecht.
Edit: I just looked at my Newkirk line again. They may have come from Slichtenhorst, Nijkerk (A regional variation?), Gelderland.