To find their way around the ocean, early modern Chinese sailors mostly relied on written sources-rutters-instead of maps and charts. The extant maps that focus on coastal and oceanic space were compiled by interested scholars and people connected to the military who aimed to defend the coast. Nevertheless, these maps include information on shallow water in a variety of ways: little dots, brief annotations, and islands labeled as "sandy." By studying selected coastal maps from the sixteenth to the early eighteenth century, this essay gives an overview of the strategies for marking shallow water. It compares the depiction of shallow water along China's coast with that for coasts farther away, where sandbanks are mapped much less consistently. As these maps were never used by sailors, the essay also argues that knowledge traveled only unilaterally, from seafarer to mapmaker, and never in the other direction.S ailing in unknown territory is a dangerous matter. Knowing the depth of the water and identifying shallow regions in particular is essential for a safe passage. To make sailing safer, sailors all over the world created maps and rutters, sharing their experience and knowledge. Early modern Chinese seafarers are no exception, and we know of rutters from the Ming (1368-1644) and Qing periods that detail routes, the time needed to sail between places, the use of the compass, and, of course, the depth of water. One early seventeenth-century observer claimed that sailors had used these rutters "since olden times" but that they were "written in slang and not easy to analyze." 1 It is probably through these rutters, in addition to what was shared orally, that seafarers transmitted their knowledge. Unfortunately-as Joseph Needham noted fifty years ago-only a few such sources on navigation survive, mostly in manuscript form, despite the long-standing tradition of printing in China. Chinese literati cared little about these seafaring matters. 2 Maps and charts, on the other hand, seem never to have been important tools for Chinese sailors-or at least the maps that survive today were not. Only with "coastal views"-drawings