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According to the United States Census Bureau, the city has a total area of 127.5 square miles (330.2 km2), of which 109.0 square miles (282.2 km2) is land and 18.5 square miles (47.9 km2) is covered by water. The old city is located on a peninsula at the point where, as Charlestonians say, "The Ashley and the Cooper Rivers come together to form the Atlantic Ocean." The entire peninsula is very low, some is landfill material, and as such, frequently floods during heavy rains, storm surges, and unusually high tides. The city limits have expanded across the Ashley River from the peninsula, encompassing the majority of West Ashley as well as James Island and some of Johns Island. The city limits also have expanded across the Cooper River, encompassing Daniel Island and the Cainhoy area. North Charleston blocks any expansion up the peninsula, and Mount Pleasant occupies the land directly east of the Cooper River.

Which city blocks Charleston for expanding up the peninsula?
North Charleston