Chistie Malrys hypersensitivity of 'debts' owed to him by society warp his view of the world. One such example is logged as: "May 1: Restriction of Movement due to Edwardian Office Block - 0.05" This entry refers to an incident which occurred crossing Hammersmith Bridge, and confronted by a building blocking his desired route. "Who made me walk this way? Who decided I should not be walking seven feet father that side, or three points west of nor-nor-east, to use the marine abbreviation? Anyone? No one? Someone must have decided. It was a conscious decision, as well. That is, they said (he said, she said), I will build here. But I think whoever it was did not also add, 'So Christy Malry shall not walk here, but shall walk there.'"

His umbrage at those responsible 'for standing this building in my way, too, limiting my freedom of movement, dictating to me where I may or may not walk in this street' is set out in his account ledger: "May 1: Scratch on Facade of Edwardian office block: 0.05"

Johnson's novel is a grand confusion of capitalism and morality, the personal and the public. It explores these issues through a logical system taken to an illogical extreme. It makes accountancy into something dark, surreal and dangerous - which I suspect is actually a more accurate picture than its usual dull image.

Christy Malry might be paranoid, but he's also right: Buildings destroy as much as they create. They restrict the infinite possibilities of a Greenfield site through the iteration of a single proposal. Architecture turns a field into a planning authority regulated, building code limited, singular thing.

Maybe architects were right when they said 'less in more'. They usually mean it when referring to buildings made out of glass and steel with minimalist detailing. However, they don't actually say what they mean by 'less' or 'more'. If they had meant 'Less architecture means more possibility' then they could have been on to something. Architecture turns landscape into concept. And that concept is embedded in the culture and society that create it.

Like most things, architecture reveals its true nature in extremes: When it's angry, aggressive, or defensive. At one extreme, a prison shows architecture that is motivated by denial. Its walls are barriers, isolating the interior from the exterior. The architectural intent is crystal clear. Architecture is performing a task of enclosure - on behalf of society, at the behest of the state. In the case of a prison, the walls enclose to isolate a piece of land. An island, not made from arrangements of land and water, but of ideologies.

The difference between the inside and outside is exaggerated. Which turns the architecture into a strange interface. One that's explored, probed, and questioned by prisoners escape attempts. Tunnels dug with spoons, hacksaws contained inside cakes, keys cast in soapbar moulds are architectural interventions, attempting to undermine the ideology of the building. This was perhaps most dramatically played out at Colditz Castle - the Second World War German prisoner of war camp. It was used to contain prisoners who had attempted escapes from other camps. On the one hand, the stone walls of the castle, the barbed wire perimeters. On the other it was riddled with all kinds of ingenious schemes to breach the architecture of captivity.

Prisons are specific and specialised. Sometimes, the scope, scale and ambition of architecture as ideology becomes vast. When ideology, identity and geography collide, it's usually on a map. At the lines drawn between one thing and another, or one place and another, or one state and another. There is an overlaying of an idea - an abstract concept - over the geological reality.

Politics, power and economics define territories. They distort landscape. We have remade the world into ideas, abstracted it into words and images - representations that have come to change the very surface of the planet. Winston Churchill remarked that 'we shape our buildings, and our buildings shape us' - but in reality, we shape maps, and the maps bash us into new shapes.

The walls of your house create a division between the city and your private domestic world, between warm and cold, wet and dry. The same fundamental construction can make barriers between other kinds of things, at other kinds of scale. The Berlin Wall erupted between two ideologies - Pushed up like a mountain range between tectonic plates made out of ideas.

The Berlin Wall may have divided a city, but it also divided the planet. Its scale was huge to begin with: Imagine a wall that divided a city. Consider the territory it partitioned : to Moscow in the East and Washington in the West. It's a wall that functioned both locally and globally. It's perhaps the most all-encompassing piece of architecture ever built. A perversion of a medieval walled city with the Warsaw ghetto.

These are failures of global politics, of societies, of religions that are played out in the form of urban design. In such extreme situation, it reveals qualities about a wall that are usually just latent. The difference between one surface and the other, the mass, height, material whose qualities prevent the passage of particular items: people or sticks or bombs.

The 'Peace Line' in Belfast is a six-meter-high steel, concrete and chain-link series of walls - flung up over decades to protect "interface communities" - flash points of sectarian violence. It separates areas such as the Catholic Falls Road from the Protestant Shankhill Road. The fences were originally intended as temporary measures when construction began in 1969. Over the years it's become taller and longer and proliferated. Though not continuous, the barriers are collectively known as a single entity. There are currently around 40 sections, with a total length of 13 miles. The bottom section of the wall is made of concrete blocks that have been painted white. On top of this is metal sheeting painted green. In parts, a metal grill attempts to prevent missiles from being thrown over the wall. At low level, scrawls of graffiti by tourists unable to comprehend divisions deep enough to result in the Peace Line.

In 2003, Israel began construction of a security wall. Following the "second intifada" in 2000, Israel faced a dramatic increase in attacks and suicide bombings. Its response was to construct a wall along the West Bank border. The barrier is still under construction. It is architecture reduced to a basic element, and made impossibly large. It's a gesture of colossal scale, demonstrating Israel's singular intent. A symbol of power. It is architecture as pre-emptive strike. If it is completed, the final barrier will run for approximately 400 miles.

If all this modern history seems depressing, lets zoom back in time to a picturesque moment in history, to the edge of the Roman Empire in AD 122, where Hadrian ordered the construction of a wall between Roman England and the Scottish tribes. Like the wall at the end of the garden, it marked the end of a domain. Except this garden was an Empire which stretched all the way back to Rome. Like the other examples, this wall was permeable: gates allowed passage through. The significance of the wall is to attempt to exert control.

When we think of architecture, we should remember that it is a set of decisions stacked up. Each of those decisions has consequences, effects both positive and negative. It's important to ask, who benefits? Asking this question is a way of revealing the ideological and political dimension of buildings. Buildings possess the strange facility of making these dimensions almost total invisible, hidden. The behaviour it encourages or discourages, the symbolism it promotes or demotes. Thankfully, most environments are not as extreme as the examples we've looked at here. Though the politics might be less extreme, it also becomes more complex. The polarisation that conflict creates obscures the more complex, faceted, graduated reality of everyday life. The way in which walls, windows, thresholds, staircases and other architectural elements reflect, embody, or indeed create these complexities. Every building is a fuzz of encoded morality, control, and social expectation. These implications are often invisible to the designer, client of a building. What Cristy Malry saw when he crossed Hammersmith Bridge was the everyday reality that at its core, architecture is the imposition of intent upon the landscape.