Voronoi cells of convergence Riemann zeta zeros

Join[Table[{-n, 0}, {n, 2, 12, 2}],
 Table[{1/2, N[Im[ZetaZero[k]]]}, {k, 1, 5}]]
<< ComputationalGeometry`
data = Join[Table[{-n, 0}, {n, 2, 32, 2}],
   Table[{1/2, Im[ZetaZero[If[k == 0, 1, k]]]}, {k, -5, 5}]];
ubd = DiagramPlot[data, LabelPoints -> False]