The phrase "eastern coastline" refers to the border or edge of land that runs along the eastern side of a body of water, typically an ocean or sea. Full definition
Location: This beach - front property sits on the south - eastern coastline of the island. (pointchaser.com)
The Tasman Peninsula, just south of Hobart in Tasmania is known for it's rugged eastern coastline located within the beautiful Tasman National Park. (stokedforsaturday.com)
Bordering Bolivia, Paraguay and Uruguay to the north and northeast, Argentina possesses a long eastern coastline which is washed by the South Atlantic Ocean. (greatrail.com)