In London Orbital, writer, walker and Londoner Iain Sinclair approaches his favourite subject – his home town – by circumambulating it. The book details his trek along the M25, London’s ring road.

Sinclair completes the 117 mile (188 km) journey in 592 pages, which works out to 5 pages per mile (or 3 per kilometer). As ring roads go, London’s is one of the longer ones – which can with some difficulty be gleaned from this map.

The map layers the peripheral highways of 27 of the world’s larger cities onto a poster, designed by the Rice School of Architecture in Houston, TX. That location is no coincidence, because the poster highlights a record for Houston: it has the largest ring road in the world (or at least the largest of all the world cities surveyed).

However, it is unclear how long a book Mr Sinclair would have to write, were he to transplant his peripatetic procedure (and the same distance-to-volume ratio) from London to Houston.

The city at the centre of the US’s sixth-largest metropolitan area (with 5.7 million inhabitants) has three ring roads: Interstate 610 [circling downtown in a 38-mile (61-km) loop], Beltway 8 [about 83 miles, or 137 km] and the as yet unfinished Grand Parkway [State Highway 99].

Clearly, for Houston to have the world’s longest loop, the big black blob on this map could only be the latter. But a few problems arise. Four, to be exact.

One: the Grand Parkway is far from finished. Only two of 11 segments are completed. However tempting it may be, it is hardly fair to tout something as “the world’s largest” before it’s been completed. Especially since, as any large-scale project, the Grand Parkway has its share of detractors. So it might never get done.

Two: even if it is to be completed, plans may change and length might vary. The website for the Grand Parkway Association doesn’t specify beyond the “circumferential scenic highway” going to be “180+ miles” (app. 290 km) long.

Three: the Houston orbital outsizes all others on this map to such an extent that it’s difficult to imagine its circumference to be no larger than London’s by a factor of 180 to 117.

And finally, four: now that I’m mentioning London’s orbital road again — the website for the UK’s Highway Agency states that the M25 is… the longest ring road in the world.

While the identity of the actual highway(s) surrounding Houston and depicted here remains elusive, it is beyond doubt that the Texan city has a large surface, a fact attested by a map posted earlier on this blog (#327), the discussion of which also touches upon the phenomenon of sprawl (large conurbations with relatively low population density) as a result of increased mobility.

 Many thanks to Owen Evans, Scott Bodenheimer, Iain Kennedy (and anyone I might have overlooked) for alerting me to this map, found here on Thumb.