Florida is a peninsula in the southeastern United States. It is the southern-most state of the 48 contiguous US states. Miami is in the south-east corner of the Florida mainland. The Florida Keys are an arc of islands that extend South and West from Miami.

The Northern-most Florida Keys align North-South next to the Miami coast (not shown in the following map), and are not directly connected by road to the rest of the Keys.

South of the Northern Keys, the Upper and Central Keys arc South-West (SW) from Key Largo to Marathon, and the Lower Keys extend WSW past Marathon:

The Upper and Central Keys separate Florida Bay from the Atlantic Ocean.

Florida Bay is a large shallow inlet of the Gulf of Mexico, with mangrove islands and average water depth of 1.5 m.

The Central Keys are an estuary, with Florida Bay as the back bay of the estuary, having average tide fluctuation of 1 meter (m) where the Bay meets the Ocean (average water level difference between high tide and low tide each day).

The ocean side of the Central Keys is itself an underwater estuary, with coral reefs 2 to 5 km offshore bounding an underwater bay of the Ocean called Hawk Channel between the reefs and the Central Keys.

Hawk Channel is deeper than Florida Bay, but much shallower than the rest of the Atlantic Ocean. The rest of the Ocean bottom drops off significantly from the edge of Hawk Channel (where the reefs are).

The volume of the Ocean next to the Keys is much greater than the volume of water in Florida Bay, causing the Ocean to have much more tide fluctuation than Florida Bay (higher high tides, and lower low tides than the Bay).

Tides go from low tide to high tide about every 6.5 hours, making the tide period approximately 13 hours (from high tide to the next high tide, and from low tide to the next low tide).

During high tide, the water surface level is higher in the Ocean than in Florida Bay, causing water to flow into the Bay through the Florida Keys from the Atlantic Ocean.

During low tide (approx. 6.5 hours after high tide), the water surface level is lower in the Ocean than in Florida Bay, causing water to flow out of Florida Bay through the Florida Keys to the Atlantic Ocean.

These changes in water flow direction happen multiple times per day, according to the tides.

Cape Sable, on the SW corner of the Florida mainland, is the focal point direction of the arc of the Florida Keys, serving as a triangulation point for connecting the Keys to the Florida survey:

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