A 3-dimensional graph-manifold is composed from simple blocks which are
products of compact surfaces with boundary by the circle. Its global structure
may be as complicated as one likes and is described by a graph which might be
an arbitrary graph. A metric of nonpositive curvature on such a manifold, if it
exists, can be described essentially by a finite number of parameters which
satisfy a geometrization equation. The aim of the work is to show that this
equation is a discrete version of the Maxwell equations of classical
electrodynamics, and its solutions, i.e., metrics of nonpositive curvature, are
critical configurations of the same sort of action which describes the
interaction of an electromagnetic field with a scalar charged field. We
establish this analogy in the framework of the spectral calculus
(noncommutative geometry) of A. Connes.