*3.1. Node Degree*

Node degree *k* is defined as the number of connections to the node and is the basic parameter for studying the topology of a complex network [24,42], as denoted by Equation (1). In Equation (1), *N* is the total number of nodes, *θij* indicates whether node *vi* and *vj* are connected or not. Here, *θij* = 1 means that *vi* and *vj* are connected, while *θij* = 0 means no connection. The average node degree of the network composed of *N* nodes is given in Equation (2). If the node is randomly selected from the network, the probability of degree *k* is *P*. Then, denote *P*(*k*) as the network degree distribution, which shows the change of *P* according to the value of *k*.

$$k(v\_i) = \sum\_{j=1}^{N} \theta\_{ij} \tag{1}$$

$$\overline{k} = \frac{1}{N} \sum\_{i=1}^{N} k(v\_i) \tag{2}$$

In the actual bus network analysis process, the node degree indicator indicates the number of bus routes directly connected to the station. The greater the node degree, the more bus lines are connected. This indicator describes the extent to which the site has a direct impact on other connected lines. The results of complex network research indicate that subsequent bus routes tend to be connected to sites with higher node degrees.
