Returns a human readable form of the RTree. Here's an example: mbr=Rectangle [x1=10.0, y1=4.0, x2=62.0, y2=85.0] mbr=Rectangle [x1=28.0, y1=4.0, x2=34.0, y2=85.0] entry=Entry [value=2, geometry=Point [x=29.0, y=4.0]] entry=Entry [value=1, geometry=Point [x=28.0, y=19.0]] entry=E
()
source not stored for this graph (policy: none)