Leeds is a city in West Yorkshire, England. Historically in Yorkshires West Riding, the history of Leeds can be traced to the 5th century when the name referred to a wooded area of the Kingdom of Elmet. The name has been applied to many administrative entities over the centuries. It changed from being the appellation of a small manorial borough in the 13th century, through several incarnations, to being the name attached to the present metropolitan borough. In the 17th and 18th centuries Leeds became a major centre for the production and trading of wool. During the Industrial Revolution, Leeds developed into a major mill town; wool was the dominant industry but flax, engineering, iron foundries, printing, and other industries were important. From being a compact market town in the valley of the River Aire in the 16th century Leeds expanded and absorbed the surrounding villages to become a populous urban centre by the mid-20th century. The main built-up area sub-division has a population of 474,632, and the City of Leeds metropolitan borough, of which it is a part, has a population of around 757,700 making it the third largest city in the United Kingdom. Today, Leeds has the most diverse economy of all the UKs main employment centres and has seen the fastest rate of private sector jobs growth of any UK city and has the highest ratio of public to private sector jobs of all the UKs Core Cities. The city has the third largest jobs total by local authority area with 480,000 in employment and self-employment at the beginning of 2015. After London, Leeds is the largest legal and financial centre in the UK, Outside of London, Leeds has the third busiest railway station and 7th busiest airport in terms of passenger numbers in England. Public transport, rail and road communications networks in the region are focused on Leeds. There are a number of twinning arrangements with towns and cities in other countries. Its assigned role in the Leeds City Region partnership recognises the citys importance to regional economic development, and the second phase of High Speed 2 plans to connect Leeds to London via East Midlands Hub and Sheffield Meadowhall.