I've entered a huge dark gallery. In each of its four corners is a glowing hemispherical earth, bearing the familiar markings and divisions of a map. Mark Wallinger's spheres are actually two-dimensional projections on to circular canvases. But they look 3-D because of shadows cast into corners of the room they lean against, and because of the perspective on the lines of latitude and longitude.

By the light of one of the projections, I read from the press release: "In 1945, members of the Johns Hopkins Physics Laboratory named the four corners of the earth as being in Ireland, south-east of the Cape of Good Hope, west of the Peruvian coast, and between New Guinea and Japan. Each of these corners (of several thousand square miles in area) is some 120ft above the geodetic mean, and the gravitational pull is measurably greater at these locations."

This is the Irish corner. In order to get it in the centre of what must be the model globe, the artist's viewpoint was from somewhere in space above the Arctic. So the Arctic Circle is at the top of the projection, and the equator runs along the bottom circumference. But that's at the receding margins of the circle, which is dominated by the Atlantic Ocean (my black shadow, for the moment) and Western Europe. This is our corner of the world, then. I draw tentative flight paths to Spain, Portugal, Greece; a winding overland route to Italy; and several short ferry trips to Amsterdam. And that's the sum of my travels abroad. Just Britain really. Pale green Britain.

The big pink area on the right is named Russia, rather than the Soviet Union. It's not a brand new map, so it's an old one - the borders were drawn before I was born. Of all the Mediterranean islands only Malta is marked, in the same-sized lettering as used for HUNG, BELG and SPAIN. So why did Mark Wallinger use a crass, out-of-date political map rather than a geodetic one which would have highlighted this four-corner idea? I walk from one corner of the globe to another. Basically it's Africa; the Americas; the Far East; and Western Europe. Maybe the map was made in 1945, following that great upheaval - that complete madness - in our corner of the world. Not forgetting a couple of atomic bombs in another.

I keep moving in a circle, and am now close to the middle of the room, where the four projectors sit on a white plinth. My shadow isn't as black as before, but it completely eclipses each corner of the globe in turn as I orbit, press release in hand ... After his trip to the moon, Buzz Aldrin was asked if he had any regrets about the mission. "I wish I had looked out of the window more," he replied. That was in the 1960s. What would Buzz have seen if he had looked out of his spaceship window? Europe recovering from itself; Japan developing at an exponential rate, thanks, perhaps, to its radioactive legacy; North America consuming everything it could get its hands on (Hollywood films, tankfuls of gas, double-layer burgers, triple-thick shakes); famine in Africa.

I keep orbiting. As soon as I eclipse one corner of the globe, my eyes move on to the next.

Chris Ofili is painting. His ancestors come from Africa, and since he made a trip to Zimbabwe, he's been using elephant dung in his celebratory pictures of black people which are now hanging in London's Tate Gallery ... On Kawara is working in his New York studio. He was born in Japan, but now works in cities worldwide. He is painting the date on a canvas - going through a familiar routine, by which the canvas is begun and finished within the same precious day - and will start on a new painting when the sun rises tomorrow... Richard Long is walking aimlessly along a country road near Bristol. But when not at home he can be found walking purposefully - making stone circles en route - almost anywhere on the planet. His wall-mounted text "A 7-DAY WALK ON THE EAST BANK OF THE RIO GRANDE" is quoted on page two of Buzz's bumper new book ...

What do we see? Men, basically. Colonising the world, but in a non-Hitleresque way that Buzz can live with.

'The Four Corners of the Earth' by Mark Wallinger: Delfina, SE1 (0171 3576600), to 22 November.

'Personal Delivery', Duncan McLaren's book is out now from Quartet (pounds 12).