Map Addict. Mike Parker

so torrential was the rain that Roy was unable to demonstrate much of their work. The King returned on 21 August and spent two hours examining the team’s work and discussing it with them. This, according to Roy, ‘met with his gracious approbation’. In his wake, all manner of society notables trotted by to see what was going on, and it was left to Sir Joseph Banks, the President of the Royal Society, to erect mobile refreshment and hospitality tents in order to cope with the crowds and to keep them at a discreet distance from the work of the surveyors. The team finally reached their destination, the workhouse at Hampton, on the penultimate day of August. By now, the steel chain had been abandoned and the entire measurement had been made using the glass rods. The base line, announced William Roy, was 27,404.72 feet: just over 5.19 miles long. ‘There never has been,’ he declaimed, ‘so great a proportion of the surface of the Earth measured with so much care and accuracy.’

      Three years later, when Ramsden’s theodolite was finally ready, the survey continued, using triangulation to work its way from Hampton down to Dover and the English Channel. The supposed aim of establishing the precise relation of the London and Paris observatories was never quite attained, but the process had, in Roy’s eyes, been hugely successful in his main ambition of showing how poor and imprecise current British maps were and how a national survey was both urgently desirable and eminently practicable. In his final report to the Royal Society and the King in 1789, Roy egged them all on:

       The trigonometrical operation, so successfully begun, should certainly be continued, and gradually extended over the whole Island. Compared with the greateness of the object, the annual expence to the publick would be a mere trifle not worthy of being mentioned. The honour of the Nation is concerned in having at least as good a map of This as there is of any Other country.

      Such as France, Your Majesty, he might have added. It took less than a year for the authorities to agree and to find the money, but, by then, Roy was dead.

      The fogs, footpads and gibbets may be long gone from Hounslow Heath, but the land still has a melancholy tang to it, if only thanks to the fact that so much of it has been eaten alive by Heathrow Airport, located there for precisely the same reasons (vast expanse, flat as a pancake, near London) as Roy’s base line. The airport has swallowed whole villages along the northern part of the line, its route south-east has been filled in with shops, factories, houses, roads and all the normal suburban detritus of the outskirts of London. The line, dotted across field and factory, and marked portentously as General Roy’s Base, used to appear on OS maps up until the early twentieth century, though not since. Strangely, the northern end of it at Heathrow is labelled, on the current OS 1:25 000 Explorer map, with the supremely wordy ‘Cannon: West End of General Roy’s Base (site of)’; although the cannon is firmly there in precisely the spot indicated, there is nothing ‘site of’ about it. The other end, at Hampton—which is far easier, and more pleasurable, to find—doesn’t even warrant that, and goes completely unmarked.

      Trying to trace the line today, I was reminded of the late Linda Smith’s immortal observation that Greater London was something of a misnomer, for ‘the further you get away from the middle of it, London doesn’t really get greater—it’s more Lesser London’. She came from Erith (‘not so much the city that never sleeps, more the town that lies awake all night staring at the ceiling’), which sits crusted on the rim of the capital in much the same way as Feltham, Bedfont and Hanworth, the sprawls that now cover William Roy’s historic line. There are other invisible lines to contend with here: these undistinguished, indistinguishable towns are firmly on the other side of the tracks from leafy Hampton (as in Court), where Roy’s measurement ended. This lies in that weird little south-western corner of Greater London, the Twickenham-Richmond triangle: smug and tweaked, embarrassed Tory so voting LibDem, death by bungalow and leylandii.

      After Major-General Roy conducted his experiments, wooden posts were interred in the ground at either end of the recorded base line as a memorial. In 1791, eleven months after Roy’s death, the party led by the Duke of Richmond, charged with re-measuring the line for the Board of Ordnance, found that the posts were rotting and so they were replaced by upended cannons. There, wondrously, they still remain. Both cannons have seen untold change unfold around them over two centuries. The southern one, at Hampton, witnessed the demolition of the borough workhouse nearby; it thence lived in an area of open ground known as Cannon Field until Twickenham Borough Council built housing estates on it in the late 1940s. At least they left the cannon intact and had the good grace to name the two nearest culde-sacs Roy Grove (where the cannon can be found sat in a grassy gap between two post-war semis) and Cannon Close (which, indeed, it is). This is Hampton as the acme of suburbia, so much so that the street opposite is Acacia Road.

      Handily, there’s a bus—the 285 Kingston-on-Thames to Heathrow—that almost precisely connects the two cannons, taking a route that’s only a little over a mile longer than William Roy’s 5.19-mile straight line. The good general wouldn’t recognise it these days. The bus coughs its way up the Uxbridge Road and into Feltham, doing a quick detour into the Sainsbury’s car park, and passing forlorn-looking light industrial estates, the Clipper Cutz hair salon, the Chirpy Chaps barbers, Cindy’s Nail Bar, Fryday’s chippy, a Subway or two, the A3 roundabout and parades of Metroland semis displaying either a St George’s flag or a ‘No To Heathrow Expansion’ sticker, sometimes both (albeit quite hard to see through the triple glazing).

      I broke my journey at Feltham, in order to take a look at another oblique memorial to William Roy, an eponymous modern pub off the High Street. This, it claims, is named after him because of its position more or less halfway along his historic line, although it’s stretching things slightly, as the General Roy pub is nearly a mile to the south of the route. There’s nothing there to indicate its homage to Roy, save for one old map of the district on the wall, showing the Feltham area as a bucolic cluster of villages, before they were entirely obliterated by the spreading gut of the capital and its main airport. The pub is pitched at workers from the nearby industrial park, home to something glassy and chromey called the Feltham Corporate Centre—a name to strike even greater terror into the loins than the town’s rather better-known Young Offenders’ Institution.

      From Feltham, the 285 fairly closely follows the route of the base line north-west towards Hatton Cross and Heathrow. Even without the growing taste of diesel in the air and the ear-splitting screams of the jets overhead, you’d know that there’s a major airport coming up. It dominates everything, especially when the tired, tatty—and increasingly impossible to sell—houses finally give way to the dispiriting landscape of international aviation: the pavement-less roads clogged with traffic, the giant hangars, mysterious metal buildings housing anything from security firms to haulage companies, car parks galore, miles of razor wire, CCTV whirring and winking in every direction and a collection of hotels that no one, surely, has ever spent a second night in.

      Heathrow Airport only came into existence thanks to government sleight-of-hand at the end of the Second World War. The site, on the richest agricultural land in the country, was commandeered under Emergency Powers in 1943, purportedly for the RAF. It was never used as such. The then Under-Secretary of State for Air, Harold Balfour, revealed in his autobiography that the requisition and construction work undertaken were entirely bogus, and that the plans had always been to turn the airfield into London’s principal civil airport come the end of hostilities. Playing the national emergency card simply allowed the authorities to circumvent any normal planning procedures—and so the pattern continues.

      Even Major-General William Roy fell foul of the airport zealots’ economy with the truth. When the never-to-be-used RAF base was being built in 1944, the memorial cannon that marked the north-western end of his base line was removed, in a theatrical attempt to demonstrate that no impediment—even one just five feet tall—should be placed in the way of our magnificent men in their flying machines. Sense eventually prevailed, and the cannon was returned in 1968, and finally replaced in its original position four years later, where it still squats. It’s not easy to locate: indeed, the irony is that you need a bloody good map to find it. Tucked away in a grassy corner nibbled out of a long-stay car park, the cannon sits alone and unloved, overlooking the airport’s main police station and the northern perimeter fence. You’d hardly notice it, especially compared with the huge banner that hangs off