The economy is an extremely important aspect of Anno 1800. The basis of a successful society is a strong economy, based, among others, on farms and plantations. Anno 1800 focuses on an interesting mechanic - instead of building many farms, one next to another, you can adjust the size of the farmland, depending on your current needs.
Once you place a farm, select it - to the left of the spinning wheel you will find information about the current number of fields. Click on the field icon and specify how much of the ground around the building you want to cultivate. This option is rather well-hidden, but it is really intuitive and allows one to save a lot of space that can be used for other purposes.