Sheffield is a city and metropolitan borough in South Yorkshire, England. Historically part of the West Riding of Yorkshire, its name derives from the River Sheaf, which runs through the city. With some of its southern suburbs annexed from Derbyshire, the city has grown from its largely industrial roots to encompass a wider economic base. The population of the City of Sheffield is In the 19th century, Sheffield gained an international reputation for steel production. Known as the Steel City, many innovations were developed locally, including crucible and stainless steel, fuelling an almost tenfold increase in the population in the Industrial Revolution. Sheffield received its municipal charter in 1843, becoming the City of Sheffield in 1893. International competition in iron and steel caused a decline in these industries in the 1970s and 1980s, coinciding with the collapse of coal mining in the area. The 21st century has seen extensive redevelopment in Sheffield along with other British cities. Sheffields gross value added has increased by 60% since 1997, standing at £9.2 billion in 2007. The economy has experienced steady growth averaging around 5% annually, greater than that of the broader region of Yorkshire and the Humber. The city is in the eastern foothills of the Pennines, and the valleys of the River Don and its four tributaries, the Loxley, the Porter Brook, the Rivelin and the Sheaf. 61% of Sheffields entire area is green space, and a third of the city lies within the Peak District national park. The city has a long sporting heritage, and is home to the worlds oldest football club, Sheffield F.C. Games between the two professional clubs, Sheffield United and Sheffield Wednesday, are known as the Steel City derby. The city is also home to the World Snooker Championship.