From the map view, you can use pinch-out to display the level of the fields and pinch-in to turn their display off.
Pinch means closing together your thumb and index finger.
Being able to see the level of the fields from around your city is useful as you don’t have to click on any field to see its level.
You can see here a bigger list of questions and answers.
If you have other questions about The Hobbit: Kingdoms of Middle-earth, leave in the comments.