Over on Facebook, Pete has an interesting question:

From which town/city of more than 50,000 inhabitants, would you pass through the most number of countries (added together) if you headed due north to the North Pole and due south to the South Pole, with an equal number of countries to the north and south of your starting point?

Well.

It's pretty clear from a casual glance at the map that the answer lies somewhere around 30° East. Indeed, Wikipedia confirms that both 27°East and 28° East pass through 21 countries:

Norway
Finland
Russia
Estonia
Latvia
Belarus
Ukraine
Moldova
Romania
Bulgaria
Turkey
Greece (Aegean islands)
Egypt
Sudan
South Sudan
Central African Republic (27° only)
Democratic Republic of the Congo
Zambia
Zimbabwe
Botswana
South Africa and
Lesotho (28° only).

So, the next question is, can we find a range of longitudes where there are 22 countries on the meridian?

Yes we can. I'm glad to report that the easternmost point of the Central African Republic is at 27°27'29.9"E, whereas the westernmost point of Lesotho is at 27°00'40.5"E. So anywhere between those two longitudes is on a meridian which passes through 22 different countries.

Actually the range is even tighter than that, and depends on the Russian islands in the Baltic – Gogland, whose easternmost point is at 27°01'43.9"E; Bolshoi Tyuters, which spreads from 27°10'32.3"E to 27°13'41.3"E; and the land frontier between Estonia and Russia, which starts at 27°19'23.9"E. So the three bands of longitude which pass through 22 countries are:

27°00'40.5"E to 27°01'43.9"E (westernmost point of Lesotho to easternmost point of Gogland)
27°10'32.3"E to 27°13'41.3"E (Bolshoi Tyuters)
27°19'23.9"E to 27°27'29.9"E (westernmost point of mainland Russia to easternmost point of Central African Republic)

(Namibia doesn't quite go far enough east to be helpful. The disputed territory of Abyei is too far east and anyway is either part of Sudan or of South Sudan. If we go far enough east for Rwanda and Burundi, we lose the Baltics. In Antarctica, Queen Maud Land is either part of Norway or not a country.)

Peter's question is a bit more demanding. If you start from the easternmost point of the island of Kos, at 27°21'21.0"E, there are parts of Turkey both north and south of you, so there are eleven countries between you and the North Pole – Norway, Finland, Estonia, Russia, Latvia, Belarus, Ukraine, Moldova, Romania, Bulgaria and Turkey – and eleven between you and the South Pole – Turkey again (I think you just scrape the tip of the Datça peninsula), Egypt, Sudan, South Sudan, Central African Republic, Democratic Republic of the Congo, Zambia, Zimbabwe, Botswana, South Africa and Lesotho.

However, Kos very clearly does not have 50,000 inhabitants – only 33,000, according to the usual sources – and the vast majority of them live further west than the end of the Datça peninsula which barely overlaps the eastern end of Kos (if at all; now I look at it more closely I'm not even sure that it does).

So I think the closest answer to Pete's question is the Turkish city of İzmir (ancient Smyrna), which has nearly three million inhabitants and parts of which definitely fall into all three ranges of longitude (it's a fairly sprawling place); it wouldn't surprise me if the İzmirians (ex-Smyrneans?) living in the ranges of 27°00'40.5"E to 27°01'43.9"E, 27°10'32.3"E to 27°13'41.3"E and 27°19'23.9"E to 27°27'29.9"E are in total many more than 50,000. They live immediately south of parts of Norway, Finland, Estonia, Russia, Latvia, Belarus, Ukraine, Moldova, Romania, and Bulgaria, which is ten countries; and immediately north of parts of Greece, Egypt, Sudan, South Sudan, Central African Republic, Democratic Republic of the Congo, Zambia, Zimbabwe, Botswana, South Africa and Lesotho, which is eleven.

There, aren’t you glad you know that?