Hexagonal boron nitride (h-BN) is a prominent member in the growing family of two-dimensional materials with potential applications ranging from being an atomically smooth support for other two-dimensional materials to templating growth of molecular layers. We have studied the structure of monolayer h-BN grown by chemical vapor deposition on Ir(111) by low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) experiments and state-of-the-art density functional theory (DFT) calculations. The lattice mismatch between the h-BN and Ir(111) surface results in the formation of a moire superstructure with a periodicity of similar to 29 angstrom and a corrugation of similar to 0.4 angstrom. By measuring the field emission resonances above the h-BN layer, we find a modulation of the work function within the moire unit cell of similar to 0.5 eV. DFT simulations for a 13-on-12 h-BN/Ir(111) unit cell confirm our experimental findings and allow us to relate the change in the work function to the subtle changes in the interaction between boron and nitrogen atoms and the underlying substrate atoms within the moire unit cell. Hexagonal boron nitride on Ir(111) combines weak topographic corrugation with a strong work function modulation over the moire unit cell. This makes h-BN/Ir(111) a potential substrate for electronically modulated thin film and heterosandwich structures.