Border police

From England, borders seem simple. There's sea. Motorway signs proclaim “Welcome to Scotland!” and “Croeso y Gymru” but passing these isn't a serious matter – even in Orkney or on Anglesey we're still in the United Kingdom.

Hadrian's Wall is a reminder of what a boundary might be but its watch-towers and forts have crumbled. Walking the path of Roman border patrols has become a challenge or delightful ramble. Sheep graze nearby and children scramble across what is left of the frontier. Like so many monuments built to control the neighbourhood, it's been reclaimed by the locals for tourism and play.

Maps tell another story. Boundaries are clear-cut – black lines that separate pink from green and yellow are as obvious as a railway track. There are even lines parcelling up the sea and white wildernesses governed by penguins and polar bears. In maps, boundaries are as unavoidable as the kiosks in which uniformed guards check and scan the passports of tourists.

Of course, I knew it was more complicated than that – just I knew there were nomadic people and people whose sense of nation and community crossed arbitrary frontiers. For years I've been fascinated by Auden's poem about the partition of India. The older Auden isn't often thought of as a radical poet but that poem is as critical as any I know about the cowardly bureaucracy of colonialism.

But I hadn't really thought about the no-man's-land crossed by migrants and patrolled by bored armed guards until I saw Ursula Biemann's video installation at Uneven Geographies, the latest exhibition at Nottingham Contemporary. Watching the guards in a nearly featureless desert, I suddenly saw the world from a perspective much closer to the migrants'.

The guards knew where the border was. There was a pile of stones here, the remnants of a building there and a railway line dividing to cross two indistinguishable pieces of ground. Sometimes the guards watched. They moved through crumbling buildings. At other times they just stood. One held a bunch of keys close to his waist. One drank water from a bottle. Dust and discarded plastic blew past them. They waited for the migrants to arrive.

The story was told of a Dutch tourist who found himself on the wrong side of the border. He was arrested and held for ten days. His belongings were confiscated. He never saw his car again. The story was routine – worth telling only because the man was an accidental migrant and a European. For those who cross frontiers these are everyday hazards.

Hunger and thirst don't stop the travellers. In another video, an imprisoned migrant told, without surprise, that ten men in his group of seventy had died of thirst when crossing the desert. The men who survived drank their own urine. They arrived and were imprisoned. They waited to be sent back – and to set out again.

Ursula Biemann's videos focus on the sub-Saharan area where the nomadic routes of the Tuareg have become the paths which migrants travel. She shows the practical demands of migrant life and the optimistic determination of travellers who are convinced life has more than poverty to offer.

Near the videos there's a series of photos of Tangier by Yto Barrada. One shows a football game on a run-down hard pitch in Tangier. The pitch is surrounded by torn wire. In the foreground a boy is making his way through a hole in the wire towards the players – it's another permeable boundary.

Between the photo and the videos, I began to see boundaries in a different way. I thought of the times when, as a child, I saw a boundary as a challenge. When my brother and I were small we liked to “go trespassing,” which meant entering any area where signs said we were forbidden. Building sites and college grounds were alluring. Most fascinating of all was an old air-raid shelter which I think we entered once – but I dreamt of it so often that dreams have obscured the reality. I can't recall exactly where the air-raid shelter was.

I still want to travel and see new places. Work and family detain me in Britain but I'm not rooted here. The film of the border guard awoke my migrant self. I realised that there aren't so many differences between me and the Africans setting out on their risky journey. I have some luck: the security provided by my red British passport and respectable appearance. I can book my journey on the internet or ask a travel agency to find me a tour and a guide.

The exhibition Uneven Geographies was worth visiting for the way it exposed and displaced my assumptions about boundaries. There's more to the exhibition than that. Delicate diagrams sketch out webs of financial power – webs so complicated it seems impossible to break free of them. The webs date back to the 1970s – it's all so much more complicated now. There are installations, photographs, displays. So many achieved a small adjustment in my way of seeing the world that, by the time I emerged, I was reeling.

Behind all the works is the net of global economic interests which holds us all. The exhibition lays bare the ways in which the rich west depends on people in other continents and the devastation of the earth. I'm haunted by new ways of seeing, in which the west is no longer central. I feel displaced from my safe, convenient way of life.

That doesn't mean I see a way out of the net. Neither vision nor analysis shows a way of adjusting the huge imbalance of power. But seeing differently still feels right and worthwhile. This is the first exhibition at Nottingham Contemporary that has changed my ideas.