  Understanding the mobility of humans and their devices is a fundamental
problem in mobile computing. While there has been much work on empirical
analysis of human mobility using mobile device data, prior work has largely
assumed devices to be independent and has not considered the implications of
modern Internet users owning multiple mobile devices that exhibit correlated
mobility patterns. Also, prior work has analyzed mobility at the spatial scale
of the underlying mobile dataset and has not analyzed mobility characteristics
at different spatial scales and its implications on system design. In this
paper, we empirically analyze the mobility of modern Internet users owning
multiple devices at multiple spatial scales using a large campus WiFi dataset.
First, our results show that mobility of multiple devices belonging to a user
needs to be analyzed and modeled as a group, rather than independently, and
that there are substantial differences in the correlations exhibited by device
trajectories across users that also need to be considered. Second, our analysis
shows that the mobility of users shows different characteristics at different
spatial scales such as within and across buildings. Third, we demonstrate the
implications of these results by presenting generative models that highlight
the importance of considering the spatial scale of mobility as well as
multi-device mobility. More broadly, our empirical results point to the need
for new modeling research to fully capture the nuances of mobility of modern
multi-device users.
