What's the wall covered by?
The wall is covered by the graffiti.
    src        edge_attr  dst
0     0           behind   10
1     0           behind    8
2     1  to the right of    8
3     1  to the right of    9
4     1       covered by    2
5     2  to the right of    9
6     2               on    1
7     2         covering    1
8     3   to the left of    8
9     3   to the left of    9
10    4               on    7
11    4   to the left of    8
12    5               on    7
13    5               by    0
14    5               on    3
15    5   to the left of    8
16    6               on    8
17    8  to the right of    4
18    8  to the right of    5
19    8      in front of    0
20    8   to the left of    1
21    8  to the right of    3
22    8               on    7
23    9  to the right of    3
24    9   to the left of    2
25    9   to the left of    1
26   10      in front of    0