Today, seven nations have maritime or island claims in the disputed South China Sea. This article historicizes the claims of one of the dispute's participants, the Socialist Republic of Vietnam. It argues that cartographic representations of its territory have their origin in the period of French rule, and locates a key moment in the formation of an Indochinese—and later Vietnamese—space encompassing the South China Sea in a series of four maps that represented research carried out by the colonial Institute of Oceanography. By recreating the biographies of these maps, the article reveals their origin in a contingent interplay of multiple factors, including global scientific networks, economic development, imperial defense, and personal research agendas. The article suggests that attention to the biographies of maps could be an effective means of deconstructing and denaturalizing many of the territorial claims that drive the dispute in the South China Sea today.