Bear in mind that in the seventy five years since then, inter-city road travel has got much faster and inter-city air travel got much cheaper (through train travel times aren't any faster and rail prices between city centres probably haven't changed much, if measured in dollars adjusted for inflation and income growth).
Air travel was fast enough - in the air - even in the 1930s to best rail and road travel times, particularly since airports could be close to city centres and security and baggage handling delays were minimal.
But it was also very expensive, infrequent and couldn't operate in the dark or in bad weather.
On balance then, today, weighing much cheaper prices and more reliable flights against airports now at city edges and all those baggage and security delays, air still remains uncompetitive between city centres less than 200 miles apart, in terms of total travel time and general hassles.
Glasgow - London Corridor
In the 1940s, as today, the north-south central urban corridor in the UK ran from Glasgow through Manchester to Birmingham to London.
A really big city's outer limits for easy commuting and easy frequent meetings is a radius about 100 miles from the city centre --- 1.5 hours traveling time by the fastest transport.
This means that a really big city needs no bigger cities closer than three hours away traveling by rail or road, city centre to city centre, (that is 1.5 hours from one plus 1.5 hours from the other) if it is to unrivalled in its bailiwick.
I argue a urban corridor on the national and international scale is a group of really big cities, each at least 3 hours apart --- but no further.
Too close and the big cities just smear into the one big national centre for everything (think Seoul in Korea) and too far apart, they might as well be on separate universes, as is the case with Australia's big cities.
It is little wonder most experts expect just to see just three really big cities on the UK central corridor route, all a good three hours travelling time apart - Glasgow, Manchester and London.
Washington - Boston Corridor
In America, the four really big cities on its North East urban corridor were (and are) : greater Boston (extending up into lower Maine and down into upper Connecticut), greater New York ( extending into lower Connecticut and upper New Jersey), greater Philadelphia extending up into southern New Jersey and down into Delaware and greater Washington-Baltimore, extending down into upper Virginia.
Again, one can see Philadelphia fading a bit as it isn't really three hours away from either New York City or Washington DC.
In Canada, the situation was different in 1940 than in 2015.
Detroit/Windsor - Montreal Corridor
Quebec City to Windsor is defined as Canada's urban corridor today, 150% longer than the 450 mile long urban corridors in the UK and the USA.
But in 1940, Quebec City was not very big an urban centre and certainly not a scientific centre, and Detroit-Windsor was very much bigger in importance than it is today and very important to, and very joined to, the Canadian economy.
So I would argue the wartime urban corridor was about the same length in Canada as in the other two countries and ran from Windsor/Detroit to Montreal, passing through places like London, Toronto, Kingston and Ottawa along the way.
Detroit Michigan-London Ontario, greater Toronto and Kingston-Ottawa-Montreal were the three (widely separated) big centres in terms of engineering/basic science/medicine expertise and government/financial power.
New York City is ideally centrally situated - 4 hours from either extreme of Boston to the north and Washington to the south.
Manchester could play the same role in the UK but in fact, in 2015 as in 1940, all big decisions are still made in the London Thames Valley region.
In 1940 Ottawa was also the central city in the Canadian urban corridor and as national capital, it held all the wartime political power but then had none of the financial, engineering or demographic power of Montreal or Toronto.
However with the Ottawa-based NRC controlling all the war's science research dollars, wartime Ottawa did mediate successfully between the three really big academic centres of Toronto, Montreal and Kingston (Queens University).
But in terms of the Canadian drug industry, it was and is located in Montreal.
In 1940 , Montreal (looking at population, financial power, manufacturing strength and academic scientific research) was almost as powerful in Canada as New York and London then were in their respective countries.
Narrow corridors - Narrow minds
These corridors really are corridors too - quite long and very very narrow.
A British national academic conference is far more likely to take place in Manchester on the corridor than immediately off the corridor in Liverpool or Leeds, nominally rivals to Manchester in (official city boundaries only) population.
One has only to try to imagine an urban corridor running along any parts of the western coast of North American, from Vancouver to San Diego to see the problems : Vancouver - Seattle work well at three hours apart as do LA and San Diego (2 - 3 hours apart) but the rest are simply too far apart from each other to form a real urban corridor.
Because the story of wartime penicillin sprawls so confusingly over many places, characters, institutions and times around the world, the spine of my re-telling of wartime penicillin and wartime science generally, will literally run (back and forth) along these three (relatively small and short) national urban corridors in the UK, USA and Canada .
Further, wartime penicillin will mostly be re-told as seen by key participants in the corridors' leading cities of New York, London and Montreal.
Insider exclusivity - outsider inclusivity
I have made this decision on how to tell my tale based upon a growing appreciation of how much the penicillin story can be told as happening between favoured insiders (individuals, institutions, firms inside the various urban corridor) and dismissed outsiders --- everyone else , everywhere else.
In general terms, the postwar discovery of massive oil in western Canada and the resulting growth in its population and wealth, the wartime and cold war relocation of military bases, military- oriented science research facilities, and military-oriented manufacturing to the south and west coasts of America, and the post 1970s opening of new universities all over the UK has somewhat reduced the power of these urban corridors since 1940.
Against this, the rusting-out of manufacturing in these three countries, usually located as often outside these corridors as within them and their replacement with the knowledge economy has usually re-bounded to the benefit to these urban corridors.
Wartime penicillin was as much as story of manufacturing as of science, so this needed to be kept in mind in imagining ourselves back 75 years ago - the urban corridors did both jobs back then, less so today.
And yes, I freely admit that the biggest outsider of the entire tale was an insider - Dr (Martin) Henry Dawson at NYC's Columbia University -that truly rare 'inside agitator' , rather than the classic 'outside agitator' of so many white southern American nightmares....