The designers liked the idea that like the 1851 Great Exhibition in London, the roof of the Symbol Zone could be a unifying entity for the expo. They did not want the constraint imposed by the London Exhibition of having everything contained under one roof, so the space frame contained only the Festival Plaza and themed pavilions. Tange compared the concept to a tree. The idea was that although the national pavilions were like individual flowers they needed to be connected to the whole via branches and a trunk. Thus the Symbol Zone became the trunk and the moving pedestrian walkways and sub-plazas became the branches. These elements were reinforced with colour, with the trunk and branches in plain white and the pavilions in their own colours that were determined by the national architects.[3]