Geography

Borders

The borders of the 13 original states were largely determined by colonial charters. Their western boundaries were subsequently modified as the states ceded their western land claims to the Federal government during the 1780s and 1790s. Many state borders beyond those of the original 13 were set by Congress as it created territories, divided them, and over time, created states within them. Territorial and new state lines often followed various geographic features (such as rivers or mountain range peaks), and were influenced by settlement or transportation patterns. At various times, national borders with territories formerly controlled by other countries (British North America, New France, New Spain including Spanish Florida, and Russian America) became institutionalized as the borders of U.S. states. In the West, relatively arbitrary straight lines following latitude and longitude often prevail, due to the sparseness of settlement west of the Mississippi River.

Once established, most state borders have, with few exceptions, been generally stable. Only two states, Missouri (Platte Purchase) and Nevada, grew appreciably after statehood. Several of the original states ceded land, over a several year period, to the Federal government, which in turn became the Northwest Territory, Southwest Territory, and Mississippi Territory. In 1791, Maryland and Virginia ceded land to create the District of Columbia (Virginia's portion was returned in 1847). In 1850, Texas ceded a large swath of land to the federal government. Additionally, Massachusetts and Virginia (on two occasions), have lost land, in each instance to form a new state.

There have been numerous other minor adjustments to state boundaries over the years due to improved surveys, resolution of ambiguous or disputed boundary definitions, or minor mutually agreed boundary adjustments for administrative convenience or other purposes. Occasionally, either Congress or the U.S. Supreme Court has had to settle state border disputes. One notable example is the case New Jersey v. New York, in which New Jersey won roughly 90% of Ellis Island from New York in 1998.

Regional grouping

States may be grouped in regions; there are many variations and possible groupings. Many are defined in law or regulations by the federal government. For example, the United States Census Bureau defines four statistical regions, with nine divisions. The Census Bureau region definition is "widely used … for data collection and analysis," and is the most commonly used classification system. Other multi-state regions are unofficial, and defined by geography or cultural affinity rather than by state lines.