  As of 2014, 54% of the earth's population resides in urban areas, and it is
steadily increasing, expecting to reach 66% by 2050. Urban areas range from
small cities with tens of thousands of people to megacities with greater than
10 million people. Roughly 12% of the global population today lives in 28
megacities, and at least 40 are projected by 2030. At these scales, the urban
infrastructure such as roads, buildings, and utility networks will cover areas
as large as New England. This steady urbanization and the resulting expansion
of infrastructure, combined with renewal of aging urban infrastructure,
represent tens of trillion of dollars in new urban infrastructure investment
over the coming decades. These investments must balance factors including
impact on clean air and water, energy and maintenance costs, and the
productivity and health of city dwellers. Moreover, cost-effective management
and sustainability of these growing urban areas will be one of the most
critical challenges to our society, motivating the concept of science- and
data-driven urban design, retrofit, and operation-that is, "Smart Cities".
