  With the wide adoption of the multi-community setting in many popular social
media platforms, the increasing user engagements across multiple online
communities warrant research attention. In this paper, we introduce a novel
analogy between the movements in the cyber space and the physical space. This
analogy implies a new way of studying human online activities by modelling the
activities across online communities in a similar fashion as the movements
among locations. First, we quantitatively validate the analogy by comparing
several important properties of human online activities and physical movements.
Our experiments reveal striking similarities between the cyber space and the
physical space. Next, inspired by the established methodology on human mobility
in the physical space, we propose a framework to study human "mobility" across
online platforms. We discover three interesting patterns of user engagements in
online communities. Furthermore, our experiments indicate that people with
different mobility patterns also exhibit divergent preferences to online
communities. This work not only attempts to achieve a better understanding of
human online activities, but also intends to open a promising research
direction with rich implications and applications.
