Work function topography maps of a heterogeneous oxide surface were produced by a scanning Kelvin probe. The specimens studied were anodically grown TiO2 films on polycrystalline titanium. The defect densities in this oxide vary from one metal grain to another, and this is responsible for the variation of work function with location over the various titanium grains. The Kelvin probe map measures the distribution of surface charge on the oxide surface, a property which influences the catalytic, corrosion, and photoelectrochemical properties of such a surface. These measurements may be extended to other thin oxide films as well.