What's the rules for 'ground network'

I found something interesting in airport’s ground network. Usually when the airport is at the border of that country.

If you look at that airport, you can find two different results.

For VVO, a far eastern city in Russia, it can show all it neighbor airports in China (JXA MDG YNJ)

For XMN, a southeast city in China, 16km away Taiwan airport (KNH) is not there in XMN’s ground network. Someone would argue the political reason between China and Taiwan, but some other Taiwan airports like CMJ, MZG are correctly shown in the ground network of XMN.

And in KNH, no Chinese airports listed in its ground network.

I want to know is there any rules/reason when given the ground network? Why it is so special for KNH? I believe it is not a military airport, and KNH is a open tourism destination as far as I know.

I am too lazy to upload the picture, just search ‘XMN’, and goto its ground network. 16km is the distance calculated by airplane performance tool.

I think all this "ground network" connections are handmade by the team. So it may be just small human errors.

Same is with Korea (South) YNY and Korea (North) FNJ.

I think its just randomly picked.

Some farther located airports are coming up in GN and nearer ones are missing.

That’s why I think its totally random.

The ground network is usually a circle of x km around the airport. If not found at least 5 airports (if I remember correctly) the circle will increased and that’s it. We then have an exlusion file where we manualy add combinations wich shall not be in a common ground network - due to political or geographical reasons. If you find something like this, please report them to us and we will have a look at it with the next data patch.

So this may result in having one airport in the other ones ground network but not viceversa…