First principal meridian  The first principal meridian is a meridian that began at the junction of the Ohio River and Great Miami River. It extends north on the boundary line between the states of Ohio and Indiana, and roughly approximates to the meridian of longitude 84° 48′ 50″ west from Greenwich. The ranges of the public surveys in the state of Ohio, west of the Scioto River, are (in part) numbered from this meridian.