Maps: sounds like a bit of a specialist subject - a bit nerdy and detached from everyday life. That was what I thought, but since I was at the British Library anyway, I thought I'd pop into the London: A Life in Maps exhibition.

Two and a half hours later, with the gallery attendants providing a chorus of vacuum cleaners, I was thrown out when the gallery closed. It had become clear that while at first thought the recording of the lines on a map marking streets and buildings might seem mechanical, it is in fact an intensely political, contested process, which tells not just the story of the physical changes in London, but also is highly informative about its social and cultural development.

There are earlier representations — the earliest being on a gold coin of 310 that commemorates London's surrender to Constantius I Chlorus, whose forces had defeated the usurper Allectus — but it is only in the middle of the 16th century that maps as we understand them start to become readily available.

One of the earliest, which survives only in fragments, was a copperplate map of late 1550s. Already, the city map is an intensely political object. This was probably commissioned from a foreign surveyor for presentation to Phillip II (Bloody Mary's husband) by German merchants, as part of their struggle to maintain trading privileges.

Another version was soon printed, known as the Agas map. It was a simplified copy with text panels boasting of London's antiquity and wealth with no mention of foreigners - almost certainly the local merchants' response.

What was included, and excluded, was also highly political. In these early maps London more or less stops at the Tower - the East End, which would over the next couple of centuries grow enormously, was unimportant, for that was where the poor lived.

It was only in the 1790s that the East End was mapped as an essential step to building the great docks of empire. It was no cause for celebration - for this recorded the houses dismissed as old, decrepit and occupied by "the poorest classes", i.e. those that would be demolished. Five thousand lost their homes.

Maps of the West End, however, started even before it existed, for it was where the wealthy had their estates. In 1584, Ralph Treswell produced map of the fields near what is now Oxford Circus, showing, among its curiosities, the lead pipes that since 1236 had run from Hyde Park to supply water to the City.