There are (so far) five sectors where you can build and expand your resort.
The first sector is accessible by anyone from the start. Each following sector requires to be unlock, by completing and claiming several achievements. The list of achievements for unlocking each sector is listed on the Achievements page.
Unlike the other sectors you don't own the land for sector 5 and need to acquire it for a fee which is connected to your actual cash flow.
The price for unlocking sector 5 is displayed in the corresponding achievement, see example below:
Note: There is a minimal price of 1 000 000€ to purchase the land. If you have a high cash balance, the price will be higher.