A major trend in human habitats is the increasing population density. Cities are a rather recent phenomenon. In fact, as late as 1850 only 15% of the US lived in urban areas. Today over 75% of us in the US and 50% of the people  on the planet live in urban areas.

Major urban problems today include

	•	lack of or deteriorating housing

	•	crime & violence

	•	poverty

	•	pollution