Long range sidescan sonar is a technique for reconnaissance of seafloor morphology. The continuity of morphologic data to ranges of 20 nautical miles makes possible regional tectonic assessments and structural analyses. Swathmap, an application of a U.S. Navy sonar system to sidescan mapping, provides mapping rates of 30–60,000 km2/day. It has identified terraces and calderas on seamounts, changes in seafloor spreading regimes from interpretation of hill lineations, and locations of major relief features. Systems such as Swathmap are becoming increasingly important for detailed seafloor mapping.