  We present a theoretical study of vortices within a harmonically trapped
Bose-Einstein condensate in a rotating optical lattice. We find that proximity
to the Mott insulating state dramatically effects the vortex structures. To
illustrate we give examples in which the vortices: (i) all sit at a fixed
distance from the center of the trap, forming a ring, or (ii) coalesce at the
center of the trap, forming a giant vortex. We model time-of-flight expansion
to demonstrate the experimental observability of our predictions.
