  In casual discussion, a stack is often described as a variety (the coarse
space) together with stabilizer groups attached to some of its subvarieties.
However, this description does not uniquely specify the stack. Our main result
shows that for a large class of stacks one typically encounters, this
description does indeed characterize them. Moreover, we prove that each such
stack can be described in terms of two simple procedures applied iteratively to
its coarse space: canonical stack constructions and root stack constructions.
  More precisely, if $\mathcal X$ is a smooth separated tame Deligne-Mumford
stack of finite type over a field $k$ with trivial generic stabilizer, it is
completely determined by its coarse space $X$ and the ramification divisor (on
$X$) of the coarse space morphism $\pi\colon \mathcal X \to X$. Therefore, to
specify such a stack, it is enough to specify a variety and the orders of the
stabilizers of codimension 1 points. The group structures, as well as the
stabilizer groups of higher codimension points, are then determined.
