If you are basing it off of -4 gmt. Then it excludes other parts of the eastern seaboard, Florida is -5 gmt. US East Coast by definition is the coast bordering the Atlantic Ocean. Although i would argue that the Gulf of Mexico is part of the North Atlantic Ocean. Therefore Texas,Louisiana,Georgia, ,Florida etc. is on the "East Coast".its in reference to the eastern US and Canada timezone -4:00 GMT, though some have taken it to mean the east coast on anything, which is quite funny