Im sure this will have been asked before but im really not sure what terminology to stick in a search to find it.

On google flights you can put in 5 departure airports and click on Map and see everywhere in the world you can fly to on Business with certain amount of stops and its really easy to see......

BUT

Is there any site that does the opposite where you can simply state your destination is Hong Kong and it then looks at all the departure airports and returns a price.

I havent seen one but also cant imagine why there isnt one. It must surely work on the same principle of a search and return value.

Anyway, can anyone help ?

I know OP posted this in the wrong forum, but I�d also like to know the answer to this, as it would be a VERY useful tool to have.

You�ll find your answer here 🔺🔴Premium Fare Deals Forum Rules🔴🔺

Apologies. I thought as I was looking for Premium deals this would be the most apt place to put it and unfortunately I didn't read the rules of every forum before posting.

Perhaps you can actually be of help and tell me where I should post a thread about Premium deals without contravening the rules. Thanks in advance.

Instead of being petty and mocking the OP - it's better not to post anything if you can't be helpful. If the Mods aren't happy with the post, they will shift it to the correct forum. Posts like these are the problem with this forum.

Too costly computationally. The matrix had this feature (within limits) and it frequently caused hangs. Google removed it after taking over the soft. Same reason it's not in GF, I'd argue

While not exactly what OP asked for, you can use skyscanner to search an entire country as departure.

For example, you can put in US as departure, and a city as destination (i.e. ATL) and then it'll show you which US cities have the cheapest flights to ATL.

Fair enough, how about a tool that knows what I like and spits out the best business class error fare for the best origin and destination for me? I am specifically looking for a transoceanic fare of $300 for 8 people.

kiwi allows this.

Useful tool, but does it work for Business class as well? I've only ever been able to get results in Economy but I might be missing something.

Kiwi.com allows you to pick multiple countries as departure. But I seldom use it cause I don�t find it well optimised for my region.

Mileage Run Discussion or Travel Tools would probably be the right place to post.
To answer your original question, no, I know of nothing like that. As noted in another post ITA Matrix used to allow something similar, but now doesn�t allow departures from different countries.

ExpertFlyer's "Flight Timetables" is exhaustive as far as flights from places to a particular place goes, but you still have to find the pricing yourself; it doesn't deliver those. I'd suggest Matrix, personally.

It's different. Both from the technical side of things and the business case/use case side of things.

The business case side of things:

Consumers who want to take a vacation but are open to destinations. Other than co-terminal situations, generally speaking consumers depart from their local home airport.
Showing them the destinations along with the price point encourages the sale. The destination view can also include paid promotion that display certain destinations/airlines more prominently.

The opposite function that you're looking for has a much narrower use case.
I can see why a Flyertalk would want it - (Find long haul international deals in Premium cabins, and willing to pay for a cheap domestic /near-by EU reposition flight).
But that's a much smaller number of users and almost no promotional revenue opportunity. Airlines certainly won't pay to promote themselves if not downright hostile with this format.

For technical side of things -
A One-to-Many relationship is easier to cache than a Many-to-Many relationship. (Airfares varies by point of sale for the same trip)
Obviously, it is doable. Just that it is more costly computationally.

Expert Flyer or another tool marketed towards frequent flyers might have a business case to do it, just like the various 3rd party award ticket searching tools. But not a priority for Google Flights or a mass-market OTA.

OP isn't asking for many-to-many; he said 1 destination airport from any origin, which is still one-to-many, or many-to-one inversely, so the difficulty isn't due to exponential edges complexity.

The real reason why it's harder is because airplane routes are a digraph. It's much easier to traverse in search of child nodes than it is to be given a child node and asked for its parent. Short of using DP, you'd have to traverse the ancestor-descendant path twice per ancestor node. If you were to visualize it, it'd look like the mythical world tree with countless roots turning each tip into yet another mirrored world tree until it refinds the starting descendant.

Easy example for other laymen:
A____B___C
^\\v ^||v v//^
_____D

• If I start from B as the origin, and I want to find all the possible destinations, I traverse to D, then from D to A & C. This is enough to prove that A, D, and C are destinations from B.
• If I start from B as the destination, and I want to find all the possible origins, I go to D. I can confirm D is an origin because I take the directed path back to B, which proves this is an origin-destination relationship of D->B. I now go from D to A. To prove that A is an origin (A->B), I must traverse, WLOG, from A back to D back to B. The same goes for C.