‘…Cinesite’s environment team decided that to give the “realest” look they would base the CG as much as possible on photographed reality. Cinesite VFX supervisor Matt Johnson and VFX photographer Aviv Yaron took extensive reference photographs of buildings in and around Philadelphia which were digitally projected onto geometry. The buildings were then placed in layouts in Nuke and fitted into the original Glasgow plates…’
http://www.comicbookmovie.com/fansites/nailbiter111/news/?a=86384