Fourprovinces,oneisland.

The island is divided into four provinces: Leinster in the east and south east, Munster in the south west, Connacht in the west and Ulster in the north. Leinster holds Dublin and the softer farmland and hills around it. Munster takes in Cork, Kerry and Clare, with long peninsulas and mountain country. Connacht runs from Galway through Mayo to Sligo and Leitrim, facing the Atlantic. Ulster spreads across nine counties, six of them in Northern Ireland.

The provinces are old groupings rather than modern administrative units, and the counties do most of the practical work. A base in one county can put several others within an easy drive. Killarney, for example, sits close to the Cork and Clare borders, and Sligo reaches into Leitrim and Mayo. Thinking in counties helps when you plan day trips, because road distances are short but driving times are often longer than the map suggests.

Choose a base by the day trips it allows, not by the number of sights nearby. A city base suits short trips and public transport, with Dublin, Cork and Galway each giving access to a wide ring of countryside. A town base suits touring, with Westport, Kilkenny and Sligo placing you on good roads in several directions. A coastal or peninsular base suits slower travel, but the roads out to the ends of peninsulas are narrow and slow.

Weather decides more than most visitors expect. The west and the hills are wetter than the east, so a week in Connemara may bring more rain than a week in Wicklow. Build in a spare day for the outdoor plans that matter most, and keep an indoor option ready. If you plan to move between bases, fewer moves with longer stays usually work better than a new town every night.

Rail links the main cities: Dublin to Cork, Galway, Limerick, Waterford, Sligo and Belfast, with Iarnród Éireann running services in the Republic and the Enterprise linking Dublin and Belfast. Coaches reach many towns the trains do not, with Bus Éireann and private operators on the main corridors and TFI Local Link buses on rural routes. Timetables change, so check with the operator before you commit to a plan.

By car, the motorway network radiates from Dublin and the main routes between cities are good. Once off those routes, expect single-carriageway roads, slow traffic behind farm vehicles and longer times than the distance suggests. Traffic drives on the left everywhere on the island. In the Republic distances are in kilometres and speeds in km/h; in Northern Ireland they are in miles and mph. Transport for Ireland has a journey planner for public transport.

The border between the Republic of Ireland and Northern Ireland runs from Carlingford Lough in the north east to Lough Foyle in the north west. Northern Ireland is part of the United Kingdom, so it uses pounds sterling, miles and mph. There are no routine checks on roads crossing the border, but the currency and the road signs change as you cross. Carry the right money and check your route before setting out.

The Causeway Coast in County Antrim is in Northern Ireland, and so is the Giant's Causeway, cared for by the National Trust. Entry rules depend on your passport: check the Irish Immigration Service for the Republic and gov.uk for Northern Ireland. Emergency numbers are 112 or 999 on both sides, and plugs are the three-pin type G throughout. The Causeway Coastal Route runs between Belfast and Derry~Londonderry.