Gravity routing is a routing protocol that uses geographical routing such as GPSR to forward packets toward regions, where topology-based routing protocol such as DSR and AODV works well. That is, packets are "gravitated" toward these regions. This hybrid approach has two advantages: first, it can improve the performance of geographical routing by taking into account the existence of such regions; second, topology-based routing is limited to only run in small regions with fewer nodes where it works well. This paper describes the basic concepts of gravity routing, discusses design and implementation considerations, and provides simulation results demonstrating the superiority of the hybrid approach in non-uniform ad hoc networks. In addition, we describe a region-management-free method for gravity routing that avoids the need of maintaining regions.