Pinning places you've visited on maps: How to do it in the real world

I have a world map on my wall. My best mate, Green, has a world map on his wall in London. Both maps are covered in cotton lines and small red pins depicting flights and destinations, and both are updated zealously according to strict rules. For instance: Pins may be placed on a map after a visit has occurred OUTSIDE an airport. Otherwise a TRANSIT is deemed to have occurred and may only be represented by a headless pin.

Long haul flight paths depicted on the map MUST conform to actual paths taken by civilian aircraft. Exaggerated lines will be censured. Map projection is NO EXCUSE. Cotton shall be black and adhere to a modest and uniform gauge. Exuberant or unnecessarily manifest twines are CONTRARY to the spirit of the enterprise.

My wife, who is not really part of this, regards the map obsession rather unkindly as a "bunch of wank". But it has history – over 39 years to be precise. Green and I met aged 11. He had a map on his bedroom wall with pins recording where his dad travelled for work; I copied the concept to record some minor travels of my own including a holiday to the US and a £10-Pom migration experiment by my parents when I was a baby. (To this day, these lines are derided by Green as "pre-natal travels".)

After university I went backpacking with Green. Something of a weird savant when it came to airline scheduling, he rose to the challenge of booking insane non-direct routes to make the lines more interesting. He practically wrote his name over the Malay Peninsula – a minor cat's cradle that's still evident on my map.

By our late 20s, Green had gone to work for airline ground staff and I'd moved to Australia. The maps entered a new and dangerous phase as each of us tried to plot more extravagant lines, plant more exotic pins and ultimately satisfy one question: whose map looks better?

Long before selfies and emails, I actually took a photo of mine, got it developed and posted it to London. On opening the envelope, Green took one look and let it fall to the floor. He stepped over the photo with its single line going off-map into Antarctic territory muttering, "you bastard".

He got the last laugh, though. At the new Millennium, I was back in London working on the travel desk of a London newspaper and secured him a job as a travel writer which saw him travelling more than ever. I left after three years but he stayed on for 14 – and today his map is sagging with great ropes of cotton, groaning with pins, a testament to the 135 countries he's visited and the 1.5 million miles he's clocked.

Green and I turn 50 this year and we still crow over a new pin, or grouse when a trip retraces over an old flight path, in fact it's the rare conversation that doesn't include the wary question, "Did y'get a new line?" Truth is, the maps are our legacy, and not because they record our travels. It's because they chart an extraordinary friendship.