At this point, you've cleared out 4 main resources (coal, clay, iron, quartz) in the location and received individual prizes for completely removing each of them. However, on the right side of the resources' menu, you can see a scale that shows that you can get an extra reward for clearing the location. The numbers underneath indicate how many objects you need to remove to fill up the scale. Keep cutting down various objects in the location (trees, grass, stones, etc.) to get more valuable prizes :)