Figure 1.

Structure of intra-urban public transport movements in Singapore. (a) Aggregated spatial interaction network across weekdays (from 19 to 23 March 2012). For simplicity, we only show the top 1% of edges with highest total interaction intensity w_ij + w_ji in an undirected manner. The grey markers show the spatial locations of transit infrastructures, including both bus stops (dots) and metro stations (circles). (b) In/out-degree distribution P(kⁱⁿ) and P(k^out) measured on the aggregated network. (c) Probability density function P(w_ij) of interaction intensity across all OD pairs. Grey dots show the original histogram and red squares correspond to a log-binned histogram. As a guide, the green line shows a power law with an exponent β = 1.74. (d) The spatial distribution of total strength of each cell. (e) Probability density function P(sⁱⁿ) of in-strength and P(s^out) of out-strength. Both of them exhibit heavy-tailed properties. (f) Symmetrical plot of sⁱⁿ and s^out. Most dots are scattered around the red line, suggesting the homogeneous inflow and outflow spatially.