  Multilevel modeling is increasingly relevant in the context of modelling and
simulation since it leads to several potential benefits, such as software reuse
and integration, the split of semantically separated levels into sub-models,
the possibility to employ different levels of detail, and the potential for
parallel execution. The coupling that inevitably exists between the sub-models,
however, implies the need for maintaining consistency between the various
components, more so when different simulation paradigms are employed (e.g.,
sequential vs parallel, discrete vs continuous). In this paper we argue that
multilevel modelling is well suited for the simulation of human mobility, since
it naturally leads to the decomposition of the model into two layers, the
"micro" and "macro" layer, where individual entities (micro) and long-range
interactions (macro) are described. In this paper we investigate the challenges
of multilevel modeling, and describe some preliminary results using prototype
implementations of multilayer simulators in the context of epidemic diffusion
and vehicle pollution.
