Sheffield is a city and metropolitan borough in South Yorkshire, England. It is so named because of its origins in a field on the River Sheaf that runs through the city. The city has grown from its largely industrial roots to encompass a wide economic base. The population of the City of Sheffield is estimated at 525,800 people (2006), and it is one of the eight largest English cities outside London, which form the English Core Cities Group. The wider Sheffield Urban Area, which extends beyond the city proper, has a population of 640,720. Sheffield obtained world-wide recognition during the 19th century for its production of steel. Many innovations in the industry were developed locally, including crucible and stainless steel. This fuelled an almost tenfold increase in the population during the Industrial Revolution. It gained its city charter in 1893 and became officially titled the City of Sheffield. International competition caused a decline in traditional local industries during the 1970s and 1980s, and at the same time the nearby national coal industry collapsed, affecting Sheffield's population. The beginning of the 21st century has seen extensive redevelopment in many UK cities, including Sheffield. The city's GVA (gross value added) increased 60 per cent in recent years and, in 2005, reached £8.2 billion. The overall economy experienced steady growth averaging around five per cent annually and, as such, has been growing at a higher rate than has been experienced in Yorkshire and the Humber in general. The city is geographically diverse, located at the confluence of five rivers, with much of the city having been built on hillsides with views into the city centre or out to the countryside. With an estimated total of over two million trees, Sheffield has more trees per person than any other city in Europe (61% of the city is greenspace). More on Sheffield