A map from 1920 of the Panama Canal showing the channel route from Colon to the city of Panama with the miles given along the route from Colon, railroad route, lakes, reservoirs, the Gatun dam, locks, and towns along the canal. The map is color-coded to show water depths, with dark blue indicating shallow water, and light blue indicating navigable water of 41 feet or more. A chart at the bottom of the map shows a profile of the isthmus with the canal system of locks and the dam necessary to reach a water-surface elevation of 85 feet to transfer ships from the Atlantic or Pacific.