The Travelcard is an inter-modal travel ticket for unlimited use on the London Underground, London Overground, Docklands Light Railway, Tramlink, London Buses and National Rail services in the Greater London area. Travelcards can be purchased for a period of time varying from one day to a year, from Transport for London, National Rail and their agents. Depending on where it is purchased, and the length of validity, a Travelcard is either printed on a paper ticket with a magnetic stripe or encoded onto a reusable contactless electronic smart card, known as an Oyster card. The cost of a Travelcard is determined by the area it covers and, for this purpose, London is divided into a number of fare zones. The Travelcard season ticket for unlimited travel on London Buses and the London Underground was launched on 22 May 1983 by London Transport. One Day Travelcards and validity on other transport modes were added from 1984 onwards. The introduction of the Travelcard caused an increase in patronage and reduced the number of tickets that needed to be purchased by passengers.