The extended Lomon-Gari-Krümpelmann model of nucleon electromagnetic form factors, which embodies ρ, ρ ′ , ω, ω ′ and φ vector meson contributions and the perturbative QCD high momentum transfer behavior has been extended to the time-like region. Breit-Wigner formulae with momentum-dependent widths have been considered for broad resonances in order to have a parametrization for the electromagnetic form factors that fulfills, in the time-like region, constraints from causality, analyticity, and unitarity.This analytic extension of the Lomon-Gari-Krümpelmann model has been used to perform a unified fit to all the nucleon electromagnetic form factor data, in the space-like and time-like region (where form factor values are extracted from e + e − ↔ N N cross sections data). The knowledge of the complete analytic structure of form factors enables predictions at extended momentum transfer, and also of time-like observables such as the ratio between electric and magnetic form factors and their relative phase.