can't place international airport cities skylines

To make the education efficient, you need to provide public transportation to education buildings. Public transport increases land value and, if built correctly, reduces traffic congestion. The budget of each mode of transportation can be adjusted separately in the Economy menu. The different modes of transportation are suitable for different purposes, and together make it possible to build a dense network of public transportation across your city. The harbors and the airport service intercity connections.

Bus and metro networks are for inner city transport while train network can service both inner-city and intercity needs (both passenger and cargo trains). There are many modes of transportation which are unlocked through milestones you can set up a bus network, dig metro tunnels, lay down tracks for passenger and cargo trains, build both passenger and cargo terminals for ships and build an airport.

Transportation is one of the services in Cities: Skylines. A harbor and cruise ship, one example of transportation in Cities: Skylines.

Can't place international airport cities skylines