I was often amazed how some small countries have a great number of WHS and some big countries not so many. Italy is more then 50 times smaller then Russia and has almost twice as many WHS. You get the idea. out of curiosity I made a comparison of several countries by area, population and number of WHS. I did not include all countries, but the ones with many sites, very big and very small countries. I think while the basic imbalance is no great surprise the specific numbers are quite impressive: I devided the population and the area by the number of WHS and while it is no surprise that the Holy See is the winner in both categories the distance to the next ranking site is impressive: While the Holy See has one WHS per 500 inhabitants, the next candidates on my list, the Marshall Islands and Saint Kitts have more then one hundred times as many per WHS. Other countries with many WHS like Greece and Portugal a thousand times more, Russia and Singapore 10'000 times more and the culturally rich India 70'000 times more with 3.5 Million people per WHS.

Country WHS Population Pop/WHS
Holy See 2 1000 500
Marshall 1 53066 53066
Saint Kitts 1 54821 54821
Andorra 1 77281 77281
Malta 3 460297 153432
Montenegro 4 642550 160638
Saint Lucia 1 178015 178015
San Marino 1 332886 332886
Cyprus 3 1170125 390042
Greece 16 10768477 673030
Portugal 15 10291027 686068
Switzerland 12 8401120 700093
Belgium 13 11358357 873720
Austria 10 8823054 882305
Czech 12 10610947 884246
Israel 9 8857000 984111
Spain 47 46698151 993578
Italy 54 60483973 1120074
Bosnia 3 3531159 1177053
France 44 67186638 1526969
Netherlands 10 17200671 1720067
Germany 44 82800000 1881818
UK 31 65648100 2117681
peru 12 32168697 2680725
Sri Lanka 8 22409381 2801173
Iran 23 81000000 3521739
Mexico 35 123675325 3533581
Russia 28 144526636 5161666
Singapore 1 5612300 5612300
Brazil 21 209129000 9958524
China 53 1403500365 26481139
India 37 1324171354 35788415

It is quite similar if you compare the area per WHS: While the Holy see has one WHS per 0.5 km2 (it is rounded up on my list) the next candidate, San Marino has more then a hundred more area per WHS and even a small country like Santa Lucia has about a thousand times more. Even the great king of the list, Italy, has more the 5000 km2 per WHS (and 10'000 as much as the Holy See), Mexico a 100'000 and Russia a Million!!!! I find the degree of uneven distribution quite mind-blowing Country Area in km2 WHS km2/WHS
Holy See 1 2 1
San Marino 61 1 61
Malta 316 3 105
Marshall 181 1 181
Saint Kitts 261 1 261
Andorra 467 1 467
Saint Lucia 617 1 617
Singapore 721 1 721
Belgium 30528 13 2348
Israel 22000 9 2445
Cyprus 9251 3 3084
Switzerland 41285 12 3440
Montenegro 13812 4 3453
Netherlands 41543 10 4154
Italy 301338 54 5580
Portugal 92212 15 6147
Czech 78866 12 6572
UK 242495 31 7822
Sri Lanka 65610 8 8201
Greece 131957 16 8247
Germany 357168 44 8117
Austria 83879 10 8388
Spain 505990 47 10766
France 640679 44 14560
Bosnia 51129 3 17043
Mexico 1972550 35 56358
Iran 1648195 23 71661
India 3287263 37 88844
Peru 1285216 12 107101
China 9596961 53 184557
Brazil 8515767 21 405512
Russia 17098246 28 610651

If you compare the two lists and skip the obvious Holy See and the very small countries which may have profited from some at-least-one-WHS-per-country-policy, Malta is quite amazing (and has still interesting tentative sites). For me also Montenegro was quite a surprise though they may not be such terrific sites and two are transnational. Belgium, Cyprus, Switzerland and Israel are very high on both lists, all before Italy on both lists. Singapore is very high-ranking per area but low per population. Russia has five times as many per population then India but six times less per area. You may get some other interesting conclusions.

Again the list is not meant to be complete but I think it is good enough to give an idea of proportions

You are definitely the man. I am also a fan of geography (and former International Geography Olympiad participant) so I had made attempts at doing such a density study some years ago, I didn't do it because of my time constraints. But when a country gets more WHS I do think on how that will fare in the field of density. Specifically, I am looking forward at the time when Russia gets below the 1 site/500.000 km2 threshold (with its 35th site).
Regarding the list, taking out the very small countries (in area and population) it shows how great is the imbalance in WH representation between different regions of the world and different countries (there are extremely clear cases, like Peru, which has been discussed previously). Examples like that of Iran show that there is potential for some previously very unrepresented countries to gain WH recognition for its significant sites (and there is still room for greater representation, as it seems).
In the case of my country, Costa Rica, it would fare in the middle-to-low density category, with 1 WHS per approximately 12.750 km2 and 1.200.000 inhabitants. I do think it has room for improvement.

Thanks, Caspar, for the interesting overview. Small countries, especially island states and small European countries are obvious candidates for a high WHS concentration. I would find it interesting to know which 2 countries have the lowest WHS concentration (per area and per population).

Area:
Russia has a 610651 ratio and is Caspar's record holder.
Greenland has a higher ratio: 722028, although it is neither an independent country nor a WH member state. With Denmark together we get a relatively unimpressive 221041.
Sudan is higher: 620494.
Chad is even higher: 642000.
And with Angola we probably have a winner: 1,246,700!!

Now to population:
India is Caspar's record holder with 35,788415.
Bangladesh is higher with 54,317186.
Here I guess Nigeria would be the winner with 92,994820!!

Yes, that is also interesting, Assif, I am just not sure I would call them winners:-)