Google Ngram: Urban and Imaginary in American and British English

What is the relationship between urban and imaginary? This is a question defining my thinking right now. One way to consider this in relation to how people are writing about these concepts. Google Ngram makes it possible to look at the relationship between these words in the works scanned by Google Books. What is the relationship these graphs suggest?  It should not be a surprise that the word urban and imaginary seem to overlap in British and American English in the late 1960s is not a surprise. By the late 1960s, many people were imagining new visions for cities. The contour of this process was evident in planning, architecture, and literature. In all those academics and creative were writing about new forms and powerful transformations that were possible and needed.  The spike in the early 1900s and then in 1940s in British English also corresponds to bigger questions of transformation and destruction in the United Kingdom. Nothing is shocking, but perhaps this visualization is a to spark conversation.

American English, 1800-2000

British English, 1800-2000