The article argues that, contrary to what is often held in academic literature, traditional fishermen had solid empirical knowledge about underwater topography long before acoustic sounding. To substantiate the argument, a large mid twentieth-century collection of place names and terms collected among coastal fishermen in Norway is explored, with the aim to demonstrate that this vocabulary reflects a detailed knowledge about underwater geography as well as advanced navigational skills. The second aim of the article is to investigate the reformatting of this knowledge when it was first transferred to national fisheries maps and secondly when it entered the International Court of Justice as part of the Norwegian fisheries case against the UK in 1951. Reformatting represents more than a new context: It shapes and changes knowledge. The present article applies this more general principle of knowledge transformation to the study of the human–ocean relationship and explores how reformatting has decisively impacted activities at sea, influenced parameters for ocean use, and been constitutive to shaping the ocean as an object of knowledge.