Project Euclid

We compare Green's function $g$ on an infinite volume, hyperbolic Riemann surface $X$ with an analogous discrete function $g_{\disc}$ on a graphical caricature $\Gamma$ of $X$. The main result, modulo technical hypotheses, is that $g$ and $g_{\disc}$ differ by at most an additive constant $C$ which depends only on the Euler characteristic of $X$. In particular, the estimate of $g$ by $g_{\disc}$ remains uniform as the geometry (i.e., the conformal structure) of $X$ varies.