vice.toolkit.J21_sf_law.area
============================

Type : float

The surface area of the star forming region in :math:`kpc^2`. In the
``milkway`` object, this is an annulus for which calculation of the
area is trivial.

Example Code
------------
>>> import vice
>>> mw = vice.milkyway(name = "example")
>>> mw.zones[0].tau_star.area
0.7853981633974483
>>> mw.zones[10].tau_star.area
16.493361431346415