This enormously greater variety is an index of the great structural complexity a semilattice can have when compared with the structural simplicity of a tree. It is this lack of structural complexity, characteristic of trees, which is crippling our conceptions of the city. To demonstrate, let us look at some modern conceptions of the city, each of which I shall show to be essentially a tree. Figure 1 . Neighbourhoods,in clusters of five, form 'villages'.
Transportation joins the villages into a new town.
The organization is a tree. Figure 2 . This 'garden city' has been broken down into superblocks. Each superblock contains schools, parks and a number of subsidiary groups of houses built around parking lots. The organization is a tree.