Oceans and seas have long been considered as distinct areas, different from one another. At the end of the eighteenth century the idea began to appear (among romantic painters and poets) that they all formed a single space that would be a ‘global ocean’. Humboldt was the first scientist to take this idea seriously and to study oceans as a ‘whole’. He drew the first map (with isotherms) which could explain why oceans had to be understood as a global climatic machine. Since then the global behaviour of the ocean has become an undisputed scientific fact and many artists have produced paintings which ‘represent’ this state of knowledge. During the same period the coast lines were not considered as a global scientific object but as a discrete series of sites, all different from one another. Tourism was partly responsible for this division of coasts as each tourist place had to show it was unique and worth being visited. Many painters helped to highlight certain sites (Hudson River, Normandy, south coast of England). Then, at the end of the twentieth century some new equations dealing with sea level allowed the idea there was something like a global coastline, responding to a global climatic forcing. Few artists today tend to work with this global idea of local coasts but some of them, taking part in scientific cruises or fieldwork, do produce a new type of image for a global coastline.