What is the sidewalk made of?
The sidewalk is made of concrete.
    src        edge_attr  dst
0     0             near    1
1     0   to the left of    5
2     0  to the right of    1
3     0  to the right of   19
4     0  to the right of   18
5     0   to the left of   13
6     0   to the left of    2
7     1   to the left of    0
8     1               by   19
9     1          next to    0
10    2  to the right of   19
11    2  to the right of   11
12    2  to the right of    6
13    2  to the right of    0
14    3  to the right of    5
15    5             near   14
16    5               on    4
17    5  to the right of    0
18    5  to the right of   11
19    5        on top of    4
20    5        riding on    4
21    5   to the left of    3
22    6  to the right of    8
23    6   to the left of    2
24    6               on    1
25    8   to the left of    6
26    8   to the left of   11
27    9  to the right of   15
28   10  to the right of   11
29   11   to the left of   12
30   11   to the left of   17
31   11   to the left of   13
32   11   to the left of    5
33   11   to the left of    2
34   11  to the right of    8
35   11   to the left of   10
36   12  to the right of   11
37   13  to the right of    0
38   13  to the right of   11
39   14          next to    5
40   14             near    5
41   15   to the left of    9
42   17  to the right of   11
43   18             near   19
44   18   to the left of    0
45   19   to the left of    0
46   19             near   18
47   19   to the left of    2