This entry gives the total number of airports with paved runways (concrete or asphalt surfaces) by length. For airports with more than one runway, only the longest runway is included according to the following five groups - (1) over 3,047 m (over 10,000 ft), (2) 2,438 to 3,047 m (8,000 to 10,000 ft), (3) 1,524 to 2,437 m (5,000 to 8,000 ft), (4) 914 to 1,523 m (3,000 to 5,000 ft), and (5) under 914 m (under 3,000 ft). Only airports with usable runways are included in this listing. Not all airports have facilities for refueling, maintenance, or air traffic control. The type aircraft capable of operating from a runway of a given length is dependent upon a number of factors including elevation of the runway, runway gradient, average maximum daily temperature at the airport, engine types, flap settings, and take-off weight of the aircraft. Airports - with unpaved runways This entry gives the total number of airports with unpaved runways (grass, dirt, sand, or gravel surfaces) by length. For airports with more than one runway, only the longest runway is included according to the following five groups - (1) over 3,047 m (over 10,000 ft), (2) 2,438 to 3,047 m (8,000 to 10,000 ft), (3) 1,524 to 2,437 m (5,000 to 8,000 ft), (4) 914 to 1,523 m (3,000 to 5,000 ft), and (5) under 914 m (under 3,000 ft). Only airports with usable runways are included in this listing. Not all airports have facilities for refueling, maintenance, or air traffic control. The type aircraft capable of operating from a runway of a given length is dependent upon a number of factors including elevation of the runway, runway gradient, average maximum daily temperature at the airport, engine types, flap settings, and take-off weight of the aircraft. Appendixes This section includes Factbook-related material by topic. Area This entry includes three subfields. Total area is the sum of all land and water areas delimited by international boundaries and/or coastlines. Land area is the aggregate of all surfaces delimited by international boundaries and/or coastlines, excluding inland water bodies (lakes, reservoirs, rivers). Water area is the sum of the surfaces of all inland water bodies, such as lakes, reservoirs, or rivers, as delimited by international boundaries and/or coastlines. Area - comparative This entry provides an area comparison based on total area equivalents. Most entities are compared with the entire US or one of the 50 states based on area measurements (1990 revised) provided by the US Bureau of the Census. The smaller entities are compared with Washington, DC (178 sq km, 69 sq mi) or The Mall in Washington, DC (0.59 sq km, 0.23 sq mi, 146 acres). B Background This entry usually highlights major historic events and current issues and may include a statement about one or two key future trends. Birth rate