  Persistence of motion is the tendency of an object to maintain motion in a
direction for short time scales without necessarily being biased in any
direction in the long term. One of the most appropriate mathematical tools to
study this behaviour is an agent-based velocity-jump process. In the absence of
agent-agent interaction, the mean-field continuum limit of the agent-based
model (ABM) gives rise to the well known hyperbolic telegraph equation. When
agent-agent interaction is included in the ABM, a strictly advective system of
partial differential equations (PDEs) can be derived at the population-level.
However, no diffusive limit of the ABM has been obtained from such a model.
Connecting the microscopic behaviour of the ABM to a diffusive macroscopic
description is desirable, since it allows the exploration of a wider range of
scenarios and establishes a direct connection with commonly used statistical
tools of movement analysis. In order to connect the ABM at the population-level
to a diffusive PDE at the population-level, we consider a generalisation of the
agent-based velocity-jump process on a two-dimensional lattice with three forms
of agent interaction. This generalisation allows us to take a diffusive limit
and obtain a faithful population-level description. We investigate the
properties of the model at both the individual and population-level and we
elucidate some of the models' key characteristic features. In particular, we
show an intrinsic anisotropy inherent to the models and we find evidence of a
spontaneous form of aggregation at both the micro- and macro-scales.
