  Large scale shadows from buildings in a city play an important role in
determining the environmental quality of public spaces. They can be both
beneficial, such as for pedestrians during summer, and detrimental, by
impacting vegetation and by blocking direct sunlight. Determining the effects
of shadows requires the accumulation of shadows over time across different
periods in a year. In this paper, we propose a simple yet efficient class of
approach that uses the properties of sun movement to track the changing
position of shadows within a fixed time interval. We use this approach to
extend two commonly used shadowing techniques, shadow maps and ray tracing, and
demonstrate the efficiency of our approach. Our technique is used to develop an
interactive visual analysis system, Shadow Profiler, targeted at city planners
and architects that allows them to test the impact of shadows for different
development scenarios. We validate the usefulness of this system through case
studies set in Manhattan, a dense borough of New York City.
