Boundaries, areas, geographic centers and altitudes of the United States and the several States with a brief record of important changes in their territory

Boundaries between countries are established by treaties made by the sovereign powers concerned.

A boundary between two States of the United States may be changed by agreement of the State legislatures, but this agreement must be approved by Congress. The United States Congress can not change a State boundary without the consent of the State, nor can two States by mutual agreement change their common boundary without the consent of Congress. The consent to a change in a boundary need not be granted by a special act but may be inferred from subsequent legislation by Congress. Several times Congress has given its consent in advance for adjoining States to fix an indefinite water boundary between them.