Cities: Skylines

So this is actually pretty simple, but requires decent amounts of money due to terraforming costs.

When you have the Airports DLC installed, load up a saved game that has plenty of money and/or build a new city with a good cushion of cash.

In game, bring up your Airports DLC tab and select the area painting tool.

Make an initial starting point and place down your airport terminal of choice. Connect your roads to the terminal and add on a concourse.

With that done you can now click on the airport terminal and in the bottom left corner under the word “income” you will see a Size number.

As you paint your district this will increase.

Get it to 25,000 and the achievement is yours! Hard to gauge, but mine took up roughly half of a map tile.

Please let me know if you downvote and how I can improve this guide.