Did you know that the whole Philadelphia traffic jam sequence from World War Z was actually filmed in Glasgow? This, and other key sequences in the film, used environments created by Cinesite.
Cinesite’s environment team decided that to give the “realest” look they would base the CG as much as possible on photographed reality. They 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.
An exciting sequence on top of a New Jersey housing project where Gerry Lane (Brad Pitt) is being chased by zombies was filmed entirely against greenscreen; the rooftop and helicopter were the only real builds.
There are actually no tower like housing projects in New Jersey, so the team created their own. The buildings in the fore to mid ground are made up from reference filmed at a housing project in Harlem projected onto geometry. Beyond this are tower-blocks from the Lower East Side and furthest from the camera is downtown New Jersey. This more distant background is taken from a large 360 degree panorama stitched together.
The elements were all brought together into Nuke, where the environment was laid out, textured, panoramas set up, sun flares and other atmospheric effects added.