People ask me why is sprawl harmful to the environment. Among other reasons, my first response is that why build on greenfields when you have so many abandoned sites waiting to be developed back to their glory days. As technology developed and industrialization changed dramatically, erstwhile bustling industrial sites fell into decay. Many of those sites still exist and can be a delight to a photographer albeit in a graphic sense.
Feast your eyes on several such abandoned sites. Never was desolation and abandonment pictured so beautifully. All that is left to be done is to clean up the sites and redevelop them to satiate our need for more urban development. Of course, green spaces sprinkled liberally would do just as well.