Over the past 20 years, urban planners, geographers, and environmentalists have pointed out the problems associated with sprawl development -  from traffic congestion to a spatial mismatch between where people live and where jobs are located to the high fiscal costs of an ever-expanding infrastructure. Solutions often focus on the internal urban environment, that is, on ways to create healthy, pedestrian-friendly cities with ample open space and human-scale design. Now a new body of research is emerging that considers not only an “inside” look at urban growth, but also its external impact on the global environment.