[benjymo]

It also should be connected to the national rail network so long distance trains go there directly. It greatly reduces time to switch trains when you're not directly from the nearest city.

Vienna did this with their airport.

[sofixa]

Yep, Paris CDG has a small version of this (high speed trains only, but this allows for connections between planes and rail to be made) which is getting expanded with a link to the regional network of the region right to the north of the airport.

[bluGill]

Only if the airport is onithe way. Overall the city center is more important so don't slow down trains for people who don't want to be at the airport.

[sealeck]

Switzerland also has this, for example there is a direct train from Zurich Airport to Geneva Airport.

[11101010001100]

It is (in theory). There is a via rail track and stop < 1 km away.

[Symbiote]

That's inadequate. I don't want to drag my luggage around the front of the terminal looking for the shuttle bus to the station, wait for it to arrive, figure out paying for the bus (if it isn't free), then wait for a train.

The railway line should go underneath the airport terminal building. If that's not possible, a covered walkway is OK. Many significant European airports are like this.

If a connection on medium/long distance trains isn't realistic, at least there should be a metro (or whatever the 'best' transport the city has, e.g. light rail).

Compare:

Mirabelle: https://www.openstreetmap.org/?mlat=45.679722&mlon=-74.03861...

Vienna: https://www.openstreetmap.org/#map=13/48.1155/16.5329