The High Seas

Historically, sailing on the High Seas has largely been a matter of educated guesswork. While one's position north or south of the equator can be determined through observation of the night sky or the height of the sun at its zenith, this gives no insight into how far east or west one has traveled. Traditionally, this was determined by regularly determining a ship's speed and calculating distance travelled based on these measurements and time elapsed; with a skilled crew and talented navigator, a ship could generally determine its position within a few hundred miles east or west. However, this method is labour intensive, requiring near constant recording of a ship's speed and heading, and even a skilled crew looking to resupply on critical supplies like fresh food and water might spend days or weeks trying to find an island tha might be no more than a few miles across. In extreme cases, an error in position might cause the loss of a ship, foundering on reefs thought to be miles away.
The recent invention of the Marine Chronometer and numerous improvements to how clockworks are produced have changed things dramatically. Now, by measuring the timing of local noon relative to noon at a calibration location, any trained navigator can find their ship's position within minutes of local noon, with an error of less than 20 miles. This led to the production of extremely accurate navigational charts, and rendered long journeys across the vast emptiness of the deep ocean a routine activity for both naval and merchant sailors.
In the years since, one of the most farfetched tall tales of the sea has been proven true. Out in the deep ocean, several vast networks of seaweed form floating "islands" that drift in ways that defy observed currents. This plant grows bulbs that can be pressed to extract smokeless oil, and its leaves can be brewed to produce an extremely nutritious tea, which has led to the construction of the Floating City, a raft that houses hundreds of workers who harvest and process these sea-masses, living off fish and the seaweed tea.