Wright's sources
Wright sketched several pictures of Broadacre City, and with his students built a large model showing what a typical area might be like. Some views can be found on the web through Google's image search.
Wright never acknowledged any intellectual debts, but he was influenced by, among others, William James, John Dewey, the economists Henry George, Thorstein Veblen and John Commons, the progressive ideas of the La Follettes, his Chicago acquaintance Jane Addams, and others who worried about the effects of centralized banking and credit during the Great Depression. Most contemporary discussions ignore the economic reforms Wright urged, which were a version of the contemporary distributionist distrust of a centralized financial system .
Stephen Grabow discusses the sources of Wright's ideas in "Frank Lloyd Wright and the American City: The Broadacres Debate," (Grabow 1977).