2. Methods
SIENA’s purpose as a simulation environment to explore urban processes from
an environmental and spatial health view is reflected in the data and methods used
to build it. To allow maximum flexibility for the user, SIENA is made up of a two-tier
data structure consisting of a core structure and contextual information (see Fig. 1).
The SIENA core structure typifies a medium-sized city in Great Britain. It is based
on terrain, land cover, transport network and population structures of real-world
cities. These four key urban components provide important information for environmental
and health analysis because they interact, both with each other and with
other, external influences. For example, there is a twofold impact of the terrain on
traffic-related air pollution: firstly as a determinant of meteorological conditions
(e.g. wind direction) and secondly as an important influence on the spatial distribution
of the road network, available building land and consequently population
density. Population density is essential to predict population exposures but is also
related to urban expansion and determines land cover change mainly from agricultural
to urban land use and consequently has indirect influence on the transport
system. Particular focus is therefore given to the interactions between these four
urban components to preserve in SIENA the complex interactions that can be
observed in the real world.
Contextual data is the second component of the SIENA structure. This is
scenario-specific data that can be added by the user as the need arises for specific