 This paper proposes a new methodology for dividing the world's coastline into distinct segments based on their geographic and hydrological features. This approach combines existing methods of segmenting the coastline into river basins, estuaries, and continental shelves, and then further refining these segments into smaller units. The resulting segmentation is called Markets, Margin and Catchment Segmentation, which consists of 45 major zones and 149 subunits. These segments can be used to better understand the connections between rivers and oceans, as well as to estimate the amount of carbon dioxide emitted from estuaries. This article was authored by G. G. Larrell, H. H. Durr, R. Lauerwald, and others.