  In a system of point vortices, there exist regions of stability around each
vortex, even if the system is chaotic. These regions are usually called
stability islands and they have a morphology that is hard to characterise. We
study and characterise them in two point vortex systems in the infinite
two-dimensional plane -- the simplest scenario -- by studying the dynamics of
passive particles in these environments. We present computations for the
perimeter and area of these islands and highlight the analytical expressions
that define their boundary.
