Using a primitive variable formulation of the finite-element method, we have compared with differences in the surface observables, such as topography and geoid, produced by single- and double-layered thermal convection. Both constant and depth-dependent viscosities have been considered. For the same Rayleigh number larger surface perturbations are produced by single-cell convection. For the same Nusselt number the magnitudes of the surface observables are greater for double-layered convection. For the same surface heat-flux, surface topographies have similar magnitudes, but the relative amplitudes of geoid anomalies depend greatly on the style of viscosity stratification. This difference in the geoid between the two systems increases with greater surface heat-flow, regardless of viscosity structure.