Despite the crucial importance of maritime transport for world trade and economic development, dedicated tools to map the evolution of vessel movements remain lacking.Such movements, especially those recorded by the maritime insurance company Lloyd's List, represent the only available information documenting the changing spatial distribution of the world's shipping routes in the last century or so. This chapter tackles the lacuna head on by discussing how this particular type of shipping data can be accurately represented on a map (see Chapter 1 for a review of the field). Such an exercise poses specific issues in terms of geovisualization, as it necessitates, among other developments, the creation of a virtual maritime grid to which port nodes and their mutual vessel flows are assigned. Beyond geomatics, this research is also an opportunity to shed new light on a vibrant research question in maritime history, namely how steam has replaced sail shipping in space and time.We extracted snapshots of global maritime flows every five years from the Lloyd's Shipping Index between 1890 and 1925 in order to test the capacity of the geoportal to visualize such flows, and at the same time verify the spatio-temporal evolution of a bi-layered maritime network. The remainder of this chapter is organized as follows: the next section discusses the scarcity of maritime data cartography until recent years in the light of general knowledge on flow mapping in geography and elsewhere. It is followed by a description of how vessel movement data had been incorporated into a dedicated visualization system. Lastly, it provides the first-ever cartographies of such movements while discussing the gaps between our results and the existing literature on the transition from sail to steam shipping.Conclusions point to a number of ways how the visualization system may be improved in the future, and how it can contribute toward addressing numerous other issues in global transport studies in general.