At it has the seventh-highest population density of any English district. According to data from 2019, the urban area has the 11th-largest population in the UK with a population of 670,000. In 2007 the European Spatial Planning Observation Network (ESPON) defined Bristol's functional urban area as including Weston-super-Mare, Bath and Clevedon with a total population of 1.04 million, the twelfth largest of the UK. Economy Bristol has a long history of trade, originally exporting wool cloth and importing fish, wine, grain and dairy products; later imports were tobacco, tropical fruits and plantation goods. Major imports are motor vehicles, grain, timber, produce and petroleum products. Since the 13th century, the rivers have been modified for docks; during the 1240s, the Frome was diverted into a deep, man-made channel (known as Saint Augustine's Reach) which flowed into the River Avon. Ships occasionally departed Bristol for Iceland as early as 1420, and speculation exists that sailors (fishermen who landed on the Canadian coast to salt/ smoke their catch) from Bristol made landfall in the Americas before Christopher Columbus or John Cabot. Beginning in the early 1480s, the Bristol Society of Merchant Venturers sponsored exploration of the North Atlantic in search of trading opportunities. In 1552, Edward VI granted a royal charter to the Merchant Venturers to manage the port. Among explorers to depart from the port after Cabot were Martin Frobisher, Thomas James, after whom James Bay, on southern coast of Hudson Bay is named, and Martin Pring, who discovered Cape Cod and the southern New England coast in 1603. By 1670 the city had 6,000tons of shipping (of which half was imported tobacco), and by the late 17th and early 18th centuries shipping played a significant role in the slave trade. During the 18th century, Bristol was Britain's second-busiest port; business was conducted in the trading area around The Exchange in Corn Street over bronze tables known as Nails. Although the Nails are cited as originating the phrase "cash on the nail" (immediate payment), the phrase was probably in use before their installation. The city's economy also relies on the aerospace, defence, media, information technology, financial services and tourism industries. The Ministry of Defence (MoD)'s Procurement Executive, later known as the Defence Procurement Agency and Defence Equipment and Support, moved to its headquarters to Abbey Wood, Filton, in 1995. This organisation, with a staff of 12,000 to 13,000, procures and supports MoD