A Licence is a geographically defined area for prospecting, exploration or extraction of petroleum resources. The North Sea Transition Authority's licensing system covers oil and gas within Great Britain, its territorial sea and on the UK Continental Shelf (UKCS). The Petroleum Act 1998 vests all rights to the nation's petroleum resources in the Crown, but the NSTA can grant licences that confer exclusive rights to 'search and bore for and get' petroleum. Licences fall into several categories. The principal distinctions are between onshore and offshore licences, and between exploration licences (which cover exploration alone) and production licences (which cover both exploration and production). The NSTA has discretion in the granting of licences to help maximise the economic recovery of the UK's oil and gas resources. Licence data is represented by 3 different datasets; Licences, Licence Blocks and Sub Areas. Licence polygons represent the whole licence and have one polygon per licence. Licenced Blocks and Sub areas represent finer divisions of these licences and may have many polygons per licence. Most Licenced Blocks are split with several sub areas, sometimes with differing operators and beneficiaries.