led to the formation of the Antrim Plateau and the Giant's Causeway, one of Ireland's three UNESCO World Heritage Sites. Ulster also has a significant drumlin belt. The geographical centre of Ulster lies between the villages of Pomeroy and Carrickmore in County Tyrone. In terms of area, County Donegal is the largest county in all of Ulster. Transport Air The province's main airport is Belfast International Airport (popularly called Aldergrove Airport), which is located at Aldergrove, 11.5 miles northwest of Belfast near Antrim. George Best Belfast City Airport (sometimes referred to as "the City Airport" or "the Harbour Airport") is another, smaller airport which is located at Sydenham in Belfast. The City of Derry Airport is located at Eglinton, east of the city of Derry. There is also Donegal Airport (), popularly known as Carrickfinn Airport, which is located in The Rosses. Rail Railway lines are run by Northern Ireland Railways (NIR). Belfast to Bangor and Belfast to Lisburn are strategically the most important routes on the network with the greatest number of passengers and largest profit margins. The Belfast-Derry railway line connecting Londonderry railway station, via Coleraine, Ballymoney, Ballymena and Antrim, with Lanyon Place and Belfast Great Victoria Street is a noted scenic route. Belfast is also connected with Carrickfergus and Larne Harbour, Portadown, Newry and onwards, via the Enterprise service jointly operated by NIR and Iarnród Éireann, to Dublin Connolly. The main railway lines linking to and from Belfast Great Victoria Street and Belfast Central are: The Derry Line and the Portrush Branch The Larne Line The Bangor Line The Portadown Line Only five Irish counties, all in Southern and Western Ulster, currently have no mainline railway. The historic Great Northern Railway of Ireland connected them. They are Cavan, Monaghan, Fermanagh, Tyrone and Donegal. A plan to re-link Sligo and Derry through Donegal has been postponed until at least 2030. Languages and dialects Most people in Ulster speak English. English is taught in all schools in the province; Irish () is taught in all schools in the counties that are part of the Republic, and in schools in Northern Ireland, almost exclusively in the Roman Catholic and Irish-medium sectors. In responses to the 2001 census in Northern Ireland 10% of the population had "some knowledge of Irish" and 4.7% could "speak, read, write and understand" Irish. Large parts of County Donegal are Gaeltacht areas where Irish is the