Ohio's geographic location has proved to be an asset for economic growth and expansion. Because Ohio links the Northeast to the Midwest, much cargo and business traffic passes through its borders on its well-developed highways. Ohio has the nation's 10th largest highway network, and is within a one-day drive of 50% of North America's population and 70% of North America's manufacturing capacity. To the North, Lake Erie gives Ohio 312 miles (502 km) of coastline, which allows for numerous seaports. Ohio's southern border is defined by the Ohio River (with the border being at the 1793 low-water mark on the north side of the river), and much of the northern border is defined by Lake Erie. Ohio's neighbors are Pennsylvania to the east, Michigan to the northwest, Ontario to the north, Indiana to the west, Kentucky on the south, and West Virginia on the southeast.

Note that Ohio is bounded by the Ohio River, but nearly all of the river itself belongs to Kentucky and West Virginia. In 1980, the U.S. Supreme Court held that, based on the wording of the cessation of territory by Virginia (which, at that time included what is now Kentucky and West Virginia), the boundary between Ohio and Kentucky (and by implication, West Virginia) is the northern low-water mark of the river as it existed in 1792. Ohio has only that portion of the river between the river's 1792 low-water mark and the present high-water mark.

The border with Michigan has also changed, as a result of the Toledo War, to angle slightly northeast to the north shore of the mouth of the Maumee River.

Much of Ohio features glaciated plains, with an exceptionally flat area in the northwest being known as the Great Black Swamp. This glaciated region in the northwest and central state is bordered to the east and southeast first by a belt known as the glaciated Allegheny Plateau, and then by another belt known as the unglaciated Allegheny Plateau. Most of Ohio is of low relief, but the unglaciated Allegheny Plateau features rugged hills and forests.

The rugged southeastern quadrant of Ohio, stretching in an outward bow-like arc along the Ohio River from the West Virginia Panhandle to the outskirts of Cincinnati, forms a distinct socio-economic unit. Known somewhat erroneously as Ohio's "Appalachian Counties" (they are actually in the Allegheny Plateau), this area's coal mining legacy, dependence on small pockets of old manufacturing establishments, and even distinctive regional dialect set this section off from the rest of the state and, unfortunately, create a limited opportunity to participate in the generally high economic standards of Ohio. In 1965 the United States Congress passed the Appalachian Regional Development Act, at attempt to "address the persistent poverty and growing economic despair of the Appalachian Region."This act defines 29 Ohio counties as part of Appalachia. While 1/3 of Ohio's land mass is part of the federally defined Appalachian region, only 12.8% of Ohioans live there (1.476 million people.)

Significant rivers within the state include the Cuyahoga River, Great Miami River, Maumee River, Muskingum River, and Scioto River. The rivers in the northern part of the state drain into the northern Atlantic Ocean via Lake Erie and the St. Lawrence River, and the rivers in the southern part of the state drain into the Gulf of Mexico via the Ohio and then the Mississippi. The worst weather disaster in Ohio history occurred along the Great Miami River in 1913. Known as the Great Dayton Flood, the entire Miami River watershed flooded, including the downtown business district of Dayton. As a result, the Miami Conservancy District was created as the first major flood plain engineering project in Ohio and the United States.

Grand Lake St. Marys in the west central part of the state was constructed as a supply of water for canals in the canal-building era of 1820–1850. For many years this body of water, over 20 square miles (52 km²), was the largest artificial lake in the world. It should be noted that Ohio's canal-building projects were not the economic fiasco that similar efforts were in other states. Some cities, such as Dayton, owe their industrial emergence to location on canals, and as late as 1910 interior canals carried much of the bulk freight of the state.

Climate

The climate of Ohio is a humid continental climate throughout most of the state except in the extreme southern counties of Ohio's Bluegrass region section which are located on the northern periphery of the humid subtropical climate and Upland South region of the United States. Summers are hot and humid throughout the State, while winters are generally cool to cold. Precipitation is moderate year-round. Severe weather is not uncommon in the State as it is a battleground between cold Arctic air and warm Gulf air for much of the year, although there are fewer tornadoes in Ohio than in states more to the west. Severe lake effect snowstorms are also not uncommon on the southeast shore of Lake Erie, which also provides a moderating effect on the climate there.

Although predominantly not in a subtropical climate, some warmer-climate flora and fauna does reach well into Ohio. For instance, a number of trees with more southern ranges, such as the blackjack oak, Quercus marilandica, are found at their northernmost in Ohio just north of the Ohio River. Also evidencing this climatic transition from a subtropical to continental climate, several plants such as the Southern magnolia (Magnolia grandiflora), Albizia julibrissin (mimosa), Crape Myrtle, and even the occasional Needle Palm are hardy landscape materials regularly used as street, yard, and garden plantings in the Bluegrass region of Ohio; but these same plants will simply not thrive in much of the rest of the State. This interesting change may be observed while traveling through Ohio on Interstate 75 from Cincinnati to Toledo; the observant traveler of this diverse state may even catch a glimpse of Cincinnati's common wall lizard, one of the few examples of permanent "subtropical" fauna in Ohio.

Records

The highest recorded temperature was 113 °F (45 °C), near Gallipolis on July 21, 1934. The lowest recorded temperature was -39 °F (-39 °C), at Milligan on February 10, 1899.

Major cities

City and metropolitan data are from the US Census Bureau's 2006 estimates:

Columbus is the capital of Ohio, near the geographic center of the state. Other Ohio cities functioning as centers of United States metropolitan areas include Akron (home of University of Akron and Goodyear Tire and Rubber Company), Canton (home of Pro Football Hall of Fame, Malone College, and The Timken Company), Cincinnati (home of University of Cincinnati), Cleveland (home of Rock and Roll Hall of Fame), Dayton (home of University of Dayton), Lima (home of University of Northwestern Ohio), Mansfield (home of Mansfield Motorsports Park), Sandusky (home of Cedar Point), Springfield (home of Wittenberg University), Toledo (home of University of Toledo), and Youngstown (home of Youngstown State University).

Note: The Cincinnati metropolitan area extends into Kentucky and Indiana, and the Youngstown metropolitan area extends into Pennsylvania.