Figure 10

After setting ϵ to 5%, approximation errors depend on the number of pivots k (y-axis) and the number of nodes n, which varies across cities (x-axis). We found that the choice of city did not have a noticeable impact. Approximation error became small in the range 100–150 (top), and we chose \(k=109\) (bottom; framed). Due to the wide range of values, note that scales (i.e. colormaps) are different