  Sustainable Development Goals are intrinsically competing, but their
embedding into urban systems furthermore emphasises such compromises, due to
spatial complexity, the non-optimal nature of such systems, and multi-objective
aspects of their agents, among other reasons. We propose in this paper to use a
stylised simulation model for systems of cities, focused on innovation
diffusion and population dynamics, to show how trade-offs may operate at such a
scale. We proceed in particular to a bi-objective optimisation of emissions and
innovation utilities, and show that no single urban optimum exists, but a
diversity of regimes forming a compromise between the two objectives.
