Vessel traffic is not uniformly distributed. The major commercial shipping lanes follow great circle routes,
or follow coast lines to minimize the distance traveled. Dozens of major ports and “megaports” handle the
majority of the traffic, but in addition hundreds of small harbors and ports host smaller volumes of traffic.
The U.S. Navy defines 521 ports and 3,762 traffic lanes in its catalog of commercial and transportation
marine traffic (Emery et al. 2001). Vessels found in areas outside major shipping lanes include fishing
vessels, military ships, scientific research ships, and recreational craft – the last typically found near shore.