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.
Vienna did this with their airport.
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