The function of a settlement is what the people who lived and worked in the settlement did or do - what the settlement is mainly used for. Settlements often have more than one function and the function of most settlements change through time.
Settlements like Portballintrae are tourist centres. In these areas many jobs and services are related to tourism. Tourists visit this area for its scenery, leisure activities and attractions. Facilities and accommodation like the caravan park have to be provided for these visiting tourists.
Larger settlements like Belfast and Londonderry have an important industrial function. In these cities there are a lot of factories and warehouses. Traditionally industrial premises would have been in the middle of the settlements but now they tend to be based on industrial estates on the outskirts of the settlement like Belfast port.
Smaller settlements like Bushmills can also have important industries attached to them. This is Bushmills' Distillery where Bushmills' Irish whiskey is made.
This is Parliament buildings at Stormont in Belfast and it is a centre of local government. A centre of government settlement contains local or national government buildings. This is where there are a lot of jobs related to the administration of the region or country.
This is Eglington near Derry city and it is an example of a residential settlement. Residential or dormitory settlements have lots of houses but few services. They are often found near larger settlements that provide a good range of jobs and amenities. People will often live in these settlements but work elsewhere. This is called commuting.
Like many settlements in the countryside, Enniskillen developed as a market town. Towns like Enniskillen grew up around a diamond or square. This is where the weekly or monthly market was held. Farmers would travel from the surrounding area to sell goods, livestock and produce. Many rural towns still hold markets, but many of these have moved to premises in the town's outskirts.
Port and harbour settlements are found along the coast and are sited at points where ships and boats can dock. Smaller coastal settlements like Kilkeel tend to be used as fishing ports.
Whereas larger ports, sited on deep inlets like Warrenpoint will also be used by ships for the import and export of goods or the transport of people.