The character of American cities has been determined not only by geographical location, but also by the availability of land and public transportation and by the type and cost of housing. This unit supplements the section of a high school course in United States history that deals with the development and growth of cities. The time periods discussed are the last decade of the nineteenth century and the first two decades of the twentieth century and the post-World War II "Baby Boom" era. The cities from which examples are taken are Houston and Chicago. Park Forest, IL is included in the discussion of the latter period. Lesson plans include a variety of activities that use books, newspapers and the Internet. The early Progressive period overlapped with the increase in geographical area of the city. This increase in physical size resulted in the disappearance of a "walking city" and the emergence of a city in which public transportation was needed to get from home to a job. The introduction of the electric trolley made it possible for families of a wide range of economic levels to get better housing in places that were further from the central part of the city. Developers built and sold homes along transportation lines. Because some firms sold architectural plans that were advertised in publications that were distributed nationally, there was a similarity found in houses built in different sections of the country. The unit examines the origins of the Houston Heights section of Houston and the Hyde Park section of Chicago. After World War II there was a built-up demand for housing throughout the country and especially in some urban areas such as Chicago and Houston. Some developers tried to construct planned communities that would meet the needs of the new post-war families. The Sharpstown area of Houston, developed by Frank Sharp, and Park Forest, IL, a Chicago suburb developed by American Community Builders are examples of these new communities.