I've completed the iterations for the London metropolitan area. Here are the results.
It took only 3 iterations to get the London metropolitan area. The 4th iteration added no new MSOA to the metro area. In comparison, researchers who have double-checked INSEE's Paris metropolitan area say it took 7 iterations to get the Paris metropolitan area. Already there we can see that the London metro area is blocked pretty quickly by neighboring urban areas which are strong enough to resist the pull of London.
The only significant urban areas that were attracted enough by the London urban area or its attracted MSOAs to enter the London metro area are: Berkhamsted and Harpenden in Hertfordshire (Hemel Hempstead and St Albans are included in the London urban area), Potters Bar also in Hertfordshire, Epping in Essex (Loughton is included in the London urban area), Swanley and Hartley in Kent (Dartford and Gravesend are included in the London urban area), and Cobham and Godalming in Surrey (Guildford is included in the London urban area).
The rest of the commuter belt reaching the 40% threshold is made up of smaller urban areas and rurban areas. "Rurban" indicates settlements which are too small to be part of an urban area, but which are the place of residence of commuters attracted by a larger urban area and are therefore not rural in the original sense (a true rural settlement is not significantly attracted by any urban area).
Toot Hill and Fyfield in Essex are examples of rurban settlements part of the London metro area. Férolles-Attilly (Seine-et-Marne) and Davron (Yvelines) are examples of rurban settlements part of the Paris metro area.
Some urban areas neighboring London fail just short of entering the London metropolitan area at the end of the iterations, for example Brentwood.
Here are some urban areas (UA) which fail to enter the London metropolitan area:
- Brentwood UA: 39.0% (i.e. 39.0% of the people living in the Brentwood UA who are in employment work in the metropolitan area of London)
- Sevenoaks UA: 38.3%
- Aveley UA (Thurrock): 38.2%
- South Ockendon UA (Thurrock): 36.6%
- Gerrards Cross UA: 36.4%
- Hertford/Ware UA: 36.2%
- Dorking UA: 34.9%
- Hatfield UA: 33.6%
- Redhill (Reigate) UA: 32.8%
- Grays UA (Thurrock): 32.7%
- Welwyn Garden City UA: 28.0%
- Slough UA: 26.0%
Keep in mind that these are not administrative districts but urban areas defined at the MSOA level. The Brentwood UA is smaller than the Borough of Brentwood. No MSOA belonging to the Borough of Brentwood make it in the London metro area. Sevenoaks UA fails to make it in the London metro area, but some MSOAs belonging to the Sevenoaks District do reach the 40% threshold to enter the London metro area (such as Swanley or Hartley) and are therefore included in the London metro area. On the other hand the Slough UA is larger than the Borough of Slough (but then even the Borough of Slough proper would not make it in the London metro area).
And for a few administrative districts:
- Medway: 20.2% (i.e. 20.2% of the people living in the district of Medway who are in employment work in the metropolitan area of London)
- Rushmoor: 19.4%
- Wokingham: 16.4%
- Luton: 15.6%
- Crawley: 10.5%
- Reading: 9.7%
Overall I've been really surprised by the weak pull of London. Of course I had always thought that places like Reading were not part of the London metro area, because they are urban centers strong enough to resist the pull of London, and I somehow expected that Slough would not make it in the London metro area after having had a quick glance at those MSOA commuting flow tables, but I frankly didn't expect that even Brentwood or Sevenoaks wouldn't make it into the London metro area!
Of course Paris also has neighboring urban areas which fail just short of making it into the Paris metro area (such as Creil UA or Senlis UA, where we're very near the 40% threshold), but these are located further away from the center of Paris than their peers around London. What we have here, is not just the fact that the green belt blocked the expansion of the London urban area, but it has also blocked the expansion of its metro area, because separate urban areas have formed that are strong enough to resist the pull of London and have their own labor markets.
This is not the only explanation though. There must be something in the pattern of employment and in the local vitality of communities in the South-East of England that make them resist the pull of London, contrary to the situation in the Paris Basin, where towns and cities tend to be weak and totally polarized by Paris. For example Meaux, an urban area of 72,000 inhabitants located as far from Notre Dame Cathedral as Rochester (Medway) from St Paul's Cathedral, a bishopric since the Roman Empire, a town which would be easily the size of Colchester or Rochester in England, is separated from the Paris urban area by some farmland, so it is its own urban area, and historically it was the capital of its own province distinct from the province of Paris, yet it sends more than 40% of its residents in employment to the Paris urban area (and that at the 1st iteration!). Medway, on the other hand, sends only 20.2% of its residents in employment to the London metro area (and only 19.1% to the London urban area at the 1st iteration).
So now, here are the results you're all anxiously waiting for.
London urban area: 2,928 km² / 9,869,043 inhabitants (March 27, 2011 census)
London metropolitan area: 3,976 km² / 10,229,887 inhabitants (March 27, 2011 census)
Paris urban area: 2,845 km² / 10,516,110 inhabitants (Jan. 1, 2011 census)
Paris metropolitan area: 17,174 km² / 12,292,895 inhabitants (Jan. 1, 2011 census)
Size of the commuter belt (INSEE definition using 40% threshold):
- London: 1,048 km² / density: 344 inh. per km²
- Paris: 14,330 km² / density: 124 inh. per km²
The London metropolitan area has less inhabitants than the Paris urban area
! I would never have imagined that. I have used rigorously the same INSEE definition for London as is used for Paris. I have double-checked the calculations and maps several times.
We can notice that the commuter belt increases the population of London by 3.7% (from urban area to metro area), whereas it increases the population of Paris by 16.9%. The land area is increased by 36% in the case of London and by 504% in the case of Paris.
74% of the London metro area's surface is the urban area. Only 17% of the Paris metro area's surface is the urban area.
So what we have is two very morphologically different metropolitan areas. This is not unexpected though. London is located in a very dense region (the south-eastern corner of England), whereas Paris is located in a low-density region (the Paris Basin). Metro areas in dense regions are always comparatively smaller than those in low-density regions, and their commuter belts tend to be small, because they are blocked by neighboring urban areas strong enough to have their own catchment areas.
In France we can see that if we compare Toulouse, which lies in a low-density region, and Lille, which lies in a very dense region. The difference between these two metro areas is very similar to the one between Paris and London. The Toulouse metro area has more inhabitants than the Lille metro area, and is usually seen as a larger city than Lille in France, but the Toulouse metro area has 1,250,251 inhabitants (Jan. 2011) over 5,381 km² of land whereas the Lille metro area has 1,159,547 inhabitants (Jan. 2011) over only 926 km² of land. If we took a territory within a 60 km radius from the center of Lille, there would be more people (in fact much more people) living inside it than within 60 km from the center of Toulouse, but that doesn't mean the Lille metro area is more populated than the Toulouse metro area. It's the same with London: there probably live more people in a 60 km radius from St Paul's Cathedral than in a 60 km radius from Notre Dame Cathedral, but that doesn't mean the London metro area is more populated than the Paris metro area, as the figures now show beyond any doubt.
Last but not least, considering that London lies in a dense region and so is limited by neighboring urban areas, its metro area of 3,976 km² is in fact quite large for a metro area in a dense region (compare Lille and its 926 km²). With 3,976 km², the London metro area is smaller than the Toulouse metro area (5,381 km²) or the Lyon metro area (6,019 km²), but it is larger than the Nantes metro area (3,302 km²), which is one of the sprawliest French metro areas in a moderately dense region. This to put things in perspective.
Next week I'll try to make a calculation for the London metropolitan area if we used a 25% commute threshold instead of INSEE's 40% threshold, to see whether London at 25% would have more inhabitants than Paris at 40% (it will not be possible to calculate a Paris metro area at 25%, because INSEE has not published detailed commuting flow data, and in any case 25% would take us pretty, pretty far... for example Beauvais or Chartres could become part of the Paris metro area at 25%).
I will also make maps showing the London urban area and its commuter belt (at 40% and hopefully also at 25% threshold).
In the meantime, these maps below show the percentage of residents in employment in each department/county who commute to Paris & inner suburbs/Inner London. The two maps are at the same scale
. This is how to read the maps: 32.9% of the residents of Seine-et-Marne who are in employment work either in the City of Paris or its inner suburbs. 31.5% of the residents of Outer London in employment work in Inner London.