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Over the years peer-to-peer (P2P) multi-hop relays have been studied for mobile ad-hoc networks (MANETs) to overcome poor signal coverage and to improve connectivity. However, for an urban environment, particularly with a sparse mobile distribution, a ground relay is not able to achieve significant benefits, mainly due to the extremely high pathloss and shadowing encountered. Dedicated airborne relay nodes, at a height of hundreds or thousands of meters, can provide much better coverage, and hence improve the connectivity, decrease the number of hops, reduce the power consumption, and support co-operative relays when integrated into mobile ad-hoc networks. An air node can also act as the sink for current wireless sensor networks (WSNs). Despite these potential advantages, the coverage from an air node located directly above an urban operating environment has not been adequately investigated in the literature. This paper compares the advantages of airborne relaying compared to more conventional peer-to-peer mobile relays. Three channel types are considered, i.e. line-of-sight (LoS), obstructed LoS (OLoS), and non-LoS (NLoS), each with their own likelihood, pathloss, and shadowing models. The practical gain pattern of a hemispheric antenna, or a directional antenna, is also carefully considered for the air node. Comparisons of the air-to-ground (A2G) channel and the mobile P2P channel demonstrate that airborne relays can enhance the coverage and reduce the power consumption significantly.