The Australian migration zone is a legal device created by the Australian Government for the purpose of Australia's visa policy and immigration policy, as the territory in which Australia's visa policy applies. The Australian migration zone covers such Australian controlled territories as the government may determine. Prior to 2001, the Australian migration zone consisted of the mainland, as well as some external territories. Norfolk Island, for example, was not part of the Australian migration zone until 2016. Under Australia’s universal visa policy, a non-citizen must hold an Australian visa within the Australian migration zone. Without such a visa, or a bridging visa, the non-citizen is an unlawful non-citizen and treated as an "unauthorised arrival". However, the main impact of the migration zone is that unauthorised arrivals outside the zone have very limited access for review by Australian courts. In the Australian government’s strategy to stem the flow of unauthorised arrivals into Australia, in September 2001, the government passed the Migration Amendment (Excision from Migration Zone) Act 2001 and the Migration Amendment (Excision from Migration Zone) (Consequential Provisions) Act 2001 which removed ("excised") a number of external territories from the Australian migration zone. The excised territories included Ashmore, Cartier, Christmas and Cocos Islands, which lay in the Indian Ocean between Indonesia and Australia. The effect of the change was to limit the ability of unauthorised arrivals arriving there, termed "offshore entry persons", to apply for a visa on arrival. However, the Minister was still empowered to grant a visa to such persons “in the public interest”. In 2010, a landmark High Court ruled that the processing procedures on Christmas Island were unlawful and unconstitutional. After these territories were excised, increasing numbers of asylum seekers attempted to reach the Australian mainland by-passing those islands. To combat this tactic, on 30 October 2012, the Australian government excised the entire Australian mainland from the Australian migration zone. The objective of the change was to limit judicial review for boat arrivals. The legislation to excise the mainland itself from the migration zone was passed by Parliament on 16 May 2013. Before the excise, asylum seekers who reached the mainland by boat could not be sent for immigration processing to offshore Australian immigration detention facilities on Nauru or Papua New Guinea's Manus Island. The excising of islands from the Australian migration zone was and remains a controversial aspect of Australian immigration policy. Refugee advocates argue that