Unity 5.5.2p4 I see a circle in Editor, The shadows in this circle will be clearer. As the chart shows:
Looks like cascaded shadows - read about them here: https://docs.unity3d.com/Manual/DirLightShadows.html Basically, there are distances where higher resolution and lower resolution shadows are used. You can adjust a few quality settings including the number of cascades and the various distances they're used.