Kelvin probe force microscopy was used to study the impact of contacts and topography on the local potential distribution on contacted, individual functionalized graphene sheets (FGS) deposited on a SiO2/Si substrate. Negligible contact resistance is found at the graphene/Ti interface and a graphene resistance of 2.3 k Omega is extracted for a single sheet with sub-mu m size. Pronounced steps in the topography, which we attribute to a variation of the spacing between graphene and substrate, result in a significant change of the local resistivity.