Today, more than 50 percent of the world’s population lives in cities. By 2050, some 75 percent will be urbanites. Future urban design will emphasize not only innovative architecture and engineering, but the environmental, health, and social aspects of city dwelling also. And the plans anticipate potential settlements beyond Earth -- Mars in particular. Justin Hollander is an internationally recognized expert on urban planning, with many academic and media contributions. He discusses the evolving concern for healthy urban design and the numerous challenges involved in this transition. Dr. Hollander also discusses his recent book on the prospect of Mars colonization: The First City on Mars: An Urban Planner’s Guide to Settling the Red Planet