Depending on who you ask, Copenhagen’s borders fall at different places. Around 1.2 million people can say they live in Greater Copenhagen, which stretches across 13 councils and 300 square kilometres, but only around 562,000 people live in Copenhagen Council, which controls the heart of Denmark’s most important metropolis.

But there are another 100,000 people living near central Copenhagen who remain outside the reach of Denmark’s biggest council. They live in Frederiksberg, a council surrounded on all sides by Copenhagen. It’s got the Copenhagen Zoo, the city’s third largest park and the lowest tax rate in Denmark. But technically, it’s not Copenhagen.

This distinction is worth pointing out ahead of the November 19 elections. Frederiksberg Council is the fifth largest of Denmark’s 98 councils in terms of population, but the smallest in surface area – a mere eight square kilometres. This island of prime real estate is the most densely populated council in Denmark and seamlessly merges with the rest of Copenhagen. It’s often difficult to know when you’ve travelled from one council to the other, but Frederiksberg has a strong cultural and political identity forged from more than 150 years of independence from Copenhagen.

READ MORE: Radikale wants Copenhagen to annexe Frederiksberg

Frederiksberg’s foundations were set in the early 18th century with the construction of Frederiksberg Palace and Gardens on top of a hill well outside the Copenhagen city limits. A town was settled at the foot of the hill and slowly transformed over the following 150 years from an agricultural village into a trading centre with small factories, shops and homes for Copenhagen’s wealthy residents who wanted to escape the city.

Copenhagen had built a series of fortifications to defend itself from attack, and a parliamentary decree prevented any permanent construction beyond these defences. But in the 1850s, parliament abandoned the policy.

The decision coincided with the industrial revolution, resulting in rapid expansion and economic growth in the two urban centres. Copenhagen and Frederiksberg were soon pressed against each other and filling out within the geographical limits of their power. Copenhagen at first started to buy up land in neighbouring councils and parishes in order to expand, but soon realised that the only solution would be to swallow them up instead.

In 1902 Copenhagen successfully managed to annexe the district of Valby to the south-west and the district of Brønshøj to the north-west. Copenhagen now surrounded Frederiksberg on all sides and it became the independent enclave that it has remained to this day.

For much of the past century, the two councils have been run by political opponents, with the Konservative party controlling the mayoral position in Frederiksberg and Socialdemokraterne doing the same in Copenhagen.

They do manage to find lots of middle-ground, however, and have co-operated to build the Copenhagen Metro as well as roll out a new city bike system this autumn.

But while the invisible border between the two may not have a practical impact on the majority of the cities’ residents or commuters, the political and administrative differences between the councils are not insignificant. For example, taxes are higher in Copenhagen and car parking is cheaper in Frederiksberg.

So before you head to the polls, find out which side of the border you live on – you might not be living in the city you thought you were!