What is the ground covered by?
The ground is covered by the gravel.
    src        edge_attr  dst
0     0   to the left of   21
1     0   to the left of   12
2     1  to the right of   21
3     2   to the left of   12
4     2   to the left of   21
..  ...              ...  ...
67   22         covering   23
68   22  to the right of   13
69   22            above   23
70   23     covered with   22
71   23       covered by   22

[72 rows x 3 columns]