Apparent Crowding

An Eccentric Anomaly: Ed Davies's Blog

Something I noticed in the days when I often flew gliders and light aeroplanes over southern England was that the amount of green space around seemed much more when viewed from above than when travelling by road or rail.

There are sampling errors both ways at play.

In light aircraft you don't tend to fly over the large built-up areas both because of the need to be able to land clear if anything goes wrong (particularly when having fewer than two engines) and because they often have airports with associated airspace nearby. This means that the light aircraft pilot gets to see a bit more green than there really is on average.

For example, gliding from Booker (near High Wycombe, NW of London) we don't tend to fly tasks in a broad arc from north east round to south, most being set between south west and north. This covers a lot more green (Buckinghamshire, Berkshire, Oxfordshire, and so on) than grey (London, Luton, …) which is really good if you want to find somewhere to land in a hurry.

On the other hand, even within this usual task area there seems to be more green when seen from above than from the roads. I think the main reason for this is a simple selection bias: roads go to where the towns are (or towns are built where the roads are or, particularly, where the roads meet).

Suppose roads and towns were built on a completely regular 10 km grid with each town being a 2 km × 2 km square centred on the road junctions:

Each town is 4 km² and sits in the middle of a 10 km × 10 km square (100 km²) so just 4% of the land is built up. Travelling along the roads, though, you spend 2 km of distance in towns for every 10 km travelled appearing to be 20% of the distance so exaggerating the impression of built-up area by a factor of five.

If the towns are actually 1 km radius circles then their areas are proportionally only π/100 of the total and the apparent exaggeration is more like 6.37 times. Similarly ribbon development (building along the roads into and out of towns) increases the effect, as do bypasses (assuming the bypass touches the edge of the town or, more likely, the town expands to fill the space available to the bypass).

My impression is that though there are very good reasons for not letting towns just sprawl indefinitely there's actually a lot of land available, even in southern England, some of which could be built on without great detriment to the overall amount of farm and natural land and that people's misapprehension that the country is crowded helps support artificially high land prices via planning restrictions.