It constitutes both a county and a municipality. The municipality of Oslo had a population of , in , while the city's greater urban area had a population of 1,, in , [ 14 ] and the metropolitan area had an estimated population of 1,, in During the Viking Age , the area was part of Viken. The city was elevated to a bishopric in and a capital under Haakon V of Norway around the year Personal unions with Denmark from to and again from to reduced its influence.
After being destroyed by a fire in , during the reign of King Christian IV , a new city was built closer to Akershus Fortress and named Christiania in honour of the king. It became a municipality formannskapsdistrikt on 1 January The city functioned as the capital of Norway during the β union between Sweden and Norway. From , the city's name was spelled Kristiania in government usage, a spelling that was adopted by the municipal authorities in , although 'Christiania' was also used.
In , the city, after incorporating the village retaining its former name, was renamed 'Oslo'. In , Oslo merged with Aker , a municipality which surrounded the capital and which was 27 times larger, thus creating the modern, much larger Oslo municipality. Oslo is the economic and governmental centre of Norway. The city is also a hub of Norwegian trade, banking, industry and shipping. It is an important centre for maritime industries and maritime trade in Europe. The city is home to many companies within the maritime sector, some of which are among the world's largest shipping companies, shipbrokers and maritime insurance brokers.
Oslo is a pilot city of the Council of Europe and the European Commission intercultural cities programme. Oslo's population was increasing at record rates during the early s, making it the fastest growing major city in Europe at the time. The municipality of Oslo has a population of , as of 1 January The total population of this agglomeration was 1,, in To the north and east, wide forested hills Marka rise above the city giving the location the shape of a giant amphitheatre.
The urban municipality bykommune of Oslo and county fylke of Oslo are two parts of the same entity, making Oslo the only city in Norway where two administrative levels are integrated. Of Oslo's total area, km 2 50 sq mi is built-up and 9. The open areas within the built-up zone amount to 22 km 2 8.
