  Double ramification loci, also known as strata of $0$-differentials, are
algebraic subvarieties of the moduli space of smooth curves parametrizing
Riemann surfaces such that there exists a rational function with prescribed
ramification over $0$ and $\infty$. We describe the closure of double
ramification loci inside the Deligne-Mumford compactification in geometric
terms.
  To a rational function we associate its exact differential, which allows us
to realize double ramification loci as linear subvarieties of strata of
meromorphic differentials. We then obtain a geometric description of the
closure using our recent results on the boundary of linear subvarieties. Our
approach yields a new way of relating the geometry of loci of rational
functions and Teichm\"uller dynamics. We also compare our results to a
different approach using admissible covers.
