Sustainability strategies for cities take many forms. This week, our guests will tell us about two of the most interesting.

Charles Loomis and Juliet Geldi are two members of the design team that conceived Waterwork for Philadelphia. They won the international competition, Urban Voids, staged by the Van Alen Institute and the Philadelphia City Parks Association to develop a compelling vision for the city's vacant lots. Also on their winning team in the competition were Gavin Riggall and Chariss McAfee.

Kenneth Yeang is determined to make high rise buildings green. His new book, Ecodesign: A Manual for Ecological Design, promotes deep green strategies for cities. Ken is a principal in the architecture firm of Llewleyn Davies and Yeang, headquartered in the U.K.

Sustainability is our topic this week on Smart City.