When you walk around the map, you may notice green leaves appear on the map. You may find green leaves in any places: parks and by the water. They appear randomly do not stay at same point longer.
What green leaves mean
Green leaves indicate a point where you can find wild Pokemon. That means if you see many points with green leaves on the map, the possibility of finding wild Pokemon is higher.
Note:
You can find and capture Pokemon at a point where there are no green leaves. Additionally, it is not necessary to see Pokemon at points with green leaves. You may see nothing once you walk to green leaves.