Bringing up this topic as I have been wondering about it for a while. I think the hotspot concept reaches it limits in areas with good infrastructure and many sites. E.g.: All sites in Berlin can be visited from Hamburg on a day trip. The train takes less than two hours and runs hourly. Same applies to Brussels and Amsterdam.

Two options I see:
1) Be complete. Probably the most helpful if you are planning a trip.
2) Reference the nearby hotspots in the hotspot. E.g. Berlin: Hamburg, Saxony Anhalt

I have my own hotspot system for personal use. Center of the hotspot is mostly an international airport. Site must be accessible from there within max 2h total travel time. I count a site to the hotspot it's easier accessible from. So in case of HAM or TXL it would be TXL for the wonderful Housing Estates as I need much less time from there.

Having been to every US and Canadian world heritage site (save for Papahānaumokuākea), I'd say that there currently aren't any hotspots in the US or Canada.

You can, in theory, visit the Statue of Liberty and Independence Hall in a single day, but that's it. If they add the Frank Lloyd Wright sites and US skyscrapers, then New York might be one.

The only place in North American would be Mexico City and maybe Havana.

Found one and send Els mail about it:

New Hotspot: San Miguel
> San Miguel
> Guanajuato
> Queretaro
> Camino Real (e.g. in San Miguel)

And in 2017 Yucatan may become one (Chitzen Itza, Comet, Uxmal, Campeche)

Okay full list of what I sent Els tonight below. Please note that the connections page is not fully up to date.

Stockholm Hotspot as discussed.
> Visby (Bus + Ferry linked. Can be done on a day trip.)

Berlin Hotspot
> Bad Muskau. Easier to reach from Germany than from Wroclav

Aquitaine Hotspot
> Vauban: La citadelle et le fort Paté et Médoc de Blaye/Cussac-Fort-Médoc

Ile de France
> Amiens (1:30h)
> Reims
> Champagne
> Le Havre
> Loire Valley (Orleans / Tours)

New Hotspot - Burgundy (Dijon) (?)
> Dijon
> Fontenay (50min)
> Vauban: Besancon
> ROYAL SALTWORKS OF ARC-ET-SENANS
> Lyon (2h train)

Provence Hotspot:
> Route of Santiago:
>> Eglise St Honorat Arles, Bouches-du-Rhône, Provence-Alpes-Côte d'Azur, France
>> ancienne abbatiale - Saint-Gilles-du-Gard, Gard, Languedoc-Roussillon, France
> Canal du Midi
>> Beziers (2h Avignon)

New Hotspot - Copenhagen Hotspot (?)
> Par Force
> Roskilde
> Kronborg
> STEVNS KLINT

Bayern Hotspot
Not working for me and I have travelled the area. Bayern is too large
for a hotspot.
> Remove Wies: Franken is really far away from Wies
> Remove Pile Dwellings
> Add Bayreuth
> Rename to Franken / North Bavaria / Nürnberg

Hamburg Hotspot
> Remove Primeval Beech Forests: It's really far away.

Frankfurt Hotspot: Frankfurt has fast train connections. Two options
Conservative:
> Remove Strasburg > Fast train connection with TGV
> Remove Stuttgart > Yes, there is a fast ICE connection.
> Remove Wartburg Castle > Yes, there is a fast ICE connection
> Remove Brühl > Closer than Köln, but not an ICE stop
Liberal:
> Add Aachen (2h ICE).
> Add Essen
General:
> Remove Maulbronn > ICE doesn't help.

New Hotspot: Baden (Karlsruhe)
> Straßburg
> Maulbronn
> Lorsch
> Stuttgart Corbusier
> Limes

Remove Hotspot: RHINELAND-PALATINATE HOTSPOT
> This is basically the Nancy Hotspot plus Rhine.
> Otherwise add Luxemburg and possiby Vauban.

Hotspot: Emilia Romana
> Add Mantua (< 2h train from Bologna)
> Florence can be done from Bologna, too. I know I did. Both.

Hotspot: Milan
> Add Genova
> Not sure Vicenza makes sense.

Hotspot: Mexico City
> Add Monarch Butterfly reserve. 1 Bus in the morning back and forth. Taxi required from town up to park.

New Extremadura Hotspot (Merida)
> Merida
> Sevilla
> Caceres
> Elvas
> Guadalupe (by car -> bus requires hotel)
> Almaden (?)

Hotspot: Andalucia
> Very large area
> Add Gibraltar (if antequera picked as center?)

New Hotspot: Valencia
> Valencia
> Rock art
> Elche
> Tarragona (2h train)
> Teruel (3h train, car less)

New Hotspot: San Miguel
> San Miguel
> Guanajuato
> Queretaro
> Camino Real (e.g. in San Miguel)

Hotspot: Tokyo
> Sites of Japan's Meiji Industrial Revolution: Narayama
> Hiraizumi. Most travellers will have the rail pass, so it's feasible.

New Hotspot: Hiroshima
> Hiroshima
> Iwami Silvermine -> Daily busses back & forth
> Itsukushima
> Himeji-Jo (< 2h with rail pass)
> Meiji: The Imperial Steel Works (Kitakyūshū, ~2h with rail pass)

Aegean Hotspot
I don't claim to be a "world expert" on Aegean Ferry timetables but I would be interested to know from which "central point" one could visit the islands of Chios, Samos, Patmos and Rhodes and return from each to it inside a day? It is currently described as "XXX".
If Samos were taken as the most likely central point then
Samos to Chios is 2hrs 40 mins twice a week. But I am not clear that you could then see Chios and get back the same day
In high season there may be Flying Dolphin return day trips from Samos to Patmos
Samos to Rhodes return isn't possible - you would probably need to go Samos - Kos, Kos - Rhodes and no way to return on the same day!

There are two comments on this topic on another hotspot thread.

In my opinion there are some current hotspots that should be removed or edited and this is one of them.

I easily did 3 sites in one shot in Iran (only 80kms):
Shushtar, Tchoga Zambil, Susa.

I don't understand what you mean nfmungard when you write "Ile de France" like a title of several sites as Le Havre, Amiens and Reims... However, in Ile de France, you have Versailles, Provins, Fontainebleau and Paris. And in Paris you have several sites of Le Corbusier, and the Tour St Jacques which is included in St Jacques de Compostelle (and many TWHS).

You also can visit some of sites around Avignon. Avignon, Arles, Orange, Pont du Gard, grotte chauvet, maybe cevennes...and probably St Jacques de Compostelle :)).

But in any case, the interest of these sites is to visit and discover them, not to pass in front of them :))...And it takes time. For southwest of Iran, 3 sites are feasible in one shot.

I've removed it

I propose to add Jiangxi Hotspot with Centre at Shangrao (the main gateway to Sanqingshan WHS). It has some overlap with Hangzhou but Huangshan and Hongcun/Xidi is more doable as a day trip from Shangrao than Hangzhou. Direct bus to Huangshan from Hangzhou is 3.5 hours, so would be a long day trip.

* Sanqingshan: 2 hours direct bus from Shangrao Railway Station to Waishuangxi Cable Car Station
* China Danxia (Longhushan): 30 mins fast train to Yingtan, then take K2 bus from Yingtan Railway to Longhushan in under an hour
* West Lake: 2 hours high speed train (8:30 AM) to Hangzhou East, then metro to West Lake
* Grand Canal (Hangzhou Section): Visit one of the urban sections of Hangzhou Grand canal. Can be combined with the West Lake visit
* Wuyishan: 30 mins fast train to Wuyishan North. Take bus for 1 hour to Wuyishan
* Hongcun and Xidi: 1 hour fast train to Huangshan North. Take bus for 1 hour to Hongcun (which also pass by Xidi)
* Huangshan: 1 hour fast train to Huangshan North. Take tourist bus to the mountain for 1 hour. (Can be combined with Hongcun or Xidi as buses to the mountains pass by these villages)

Note: Lushan: Doable but very long day trip and involves train transfer to Nanchang. There is also one fast train from Shangrao to Jiujiang that departs around 10:00 Am and takes slightly over 2 hours.

The fast train connection from Shangrao is frequent as it's at the juncture of 2 high speed train lines.

Nice one. Would give me 4 new WHS! With the fast train connections in China, there's no shortage of hotspots there as well.

Suggested was this one:
Mumbai can now qualify as a hotspot: CST, VGADEM, Elephanta Cave, and the Western Ghats on the Maharashtra side

But I don't believe you can travel from and to Koyna Wildlife Sanctuary (western ghats) within a day from Mumbai. Any experiences / ideas?

I had investigated this immediately after the Mumbai inscription - Koyna is almost 300 kms and 6 hours by road from Mumbai (plus Mumbai traffic uncertainty) one way! I had considered making Pune the centre. It could (just about!) be done but it would be perverse to travel from Pune 2hrs 50 mins each way to the other Mumbai WHS every day and you would be at Koyna in the middle of the day only - not really a practical approach to seeing its value!

On which matter - I note that Turin has been added as a Hot Spot -but it virtually duplicates Milan - with only Ivrea as new!! And that is only 1hr 30 mins from Milan. Milan already has Portovenere - an improbable 3 hr 30 mins away!!! And Turin is itself already inside the Milan hotspot!!
We could start listing every city in an area and virtually duplicating many Hot Spots just to pick up 1 or 2 extra sites (and not even the case here)!.

I'm happy to have Turin as a hotspot. Earlier this year, we actually used it as a base for a few days to visit the Palaces in Turin, the Piedmont Vineyards and Ivrea (in anticipation of the listing). It's really well suited for visiting those sites, rather than basing in Milan.

I am sure it is a great place to use as a "centre" (we too have used it) but we don't, for instance, have separate Hotspots for each of Liverpool. Manchester, Leeds and Sheffield - all of which could perfectly well operate as "Hotspot centres" for seeing the WHS of Northern UK/Southern Scotland . We have 1 Hotspot which is titled "Northern England". It currently says "Centre - Leeds or Sheffield". (could just as easily mention all 4 cities)
We could rename Milan to e.g NW Italy and list its potential centres as Milan, Turin....... Travellers can decide which centre suits them best.
If we start duplicating Hotspots a few kms away from each other but with virtually the same WHS within them where do we stop??
If we keep both we should add Ivrea to Milan as well - and I would still question the utility of including Portovenere etc in the Milan one.