What's the ground made of?
The ground is made of concrete.
    src        edge_attr  dst
0     0           behind   11
1     1  to the right of    7
2     1   to the left of   13
3     1   to the left of   12
4     2  to the right of    5
5     2  to the right of    6
6     2   to the left of   14
7     3           beside    0
8     4           beside    7
9     4   to the left of    8
10    4   to the left of    6
11    5   to the left of   11
12    5   to the left of    2
13    5   to the left of    6
14    5   to the left of    8
15    6   to the left of   13
16    6   to the left of   12
17    6  to the right of    5
18    6  to the right of    4
19    6   to the left of    2
20    6   to the left of   11
21    6   to the left of    9
22    6   to the left of   10
23    6   to the left of   14
24    6  to the right of    7
25    7   to the left of    1
26    7   to the left of    6
27    7   to the left of    8
28    7   to the left of   11
29    8  to the right of    4
30    8  to the right of    5
31    8   to the left of   11
32    8  to the right of    7
33    8   to the left of   13
34    8   to the left of   12
35    9   to the left of   12
36    9   to the left of   10
37    9  to the right of    6
38   10  to the right of    6
39   10   to the left of   14
40   10  to the right of    9
41   11      in front of    0
42   11  to the right of    5
43   11  to the right of    6
44   11  to the right of    7
45   11  to the right of    8
46   12  to the right of    1
47   12  to the right of    6
48   12  to the right of    8
49   12  to the right of    9
50   13  to the right of    8
51   13  to the right of    6
52   13  to the right of    1
53   14  to the right of    2
54   14  to the right of   10
55   14  to the right of    6