# Applying Spectral Clustering to Decode Mobility Patterns in Athens, Greece
## 3 Results  
From the clustering process, 6 clusters emerged. The pie in Figure 1 gives the share of trips allocated in each cluster. As can be observed, the Cluster 2 and 4 report the highest percentage of trips of 39.0% and 28.4%, respectively. The sum of other clusters' share does not exceed the 33% (i.e., approximately the 1/3 of the sample). These clusters represent distinct types of trips that are performed daily in Athens, Greece. It comprises an alternative way to classify trips and understand mobility. The first cluster consists of 108 reported trips (8.02%), 42% of which appear to involve walking (see Figure 2). Indeed, 65% of the trips in this group are conducted either by walking or by bus, while 85% of the total trips are made by walking, bus, or trains. Thus, the majority of trips in this cluster are carried out by transport modes that are more \"environmentally friendly.\" Regarding the purpose of trips included in the first cluster, it is observed that 48% of them are for recreation. Furthermore, at least 75% of the trips begin during the afternoon and evening hours, between 16:00 and 22:00 (see Figure 3). The peak hour of these trips is at 21:00. Also, in this cluster, the travel distance shows a mean value of about 1687 m (see Figure 4). Also, 75% of the trips of the cluster have a distance of less than or equal to 5 km. Considering these attributes, it is concluded that the trips of the first cluster concern intra-zonal movements or movements to neighboring or adjacent zones of Athens. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Variable** & **Type** & **Description** \\  & & **(Levels) (If Categorical Variable)** \\ \hline Variables that are used to interpret the clusters & & \\ gender & categorical & \{female, male\} \\ age group & categorical & [18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 4  
The second cluster incorporates 525 trips, i.e., 38.98% of the total observations of the sample. Private cars dominate as the mode of transport, accounting for 47% of the total trips that are included. In other words, half of the trips in the second cluster are made by car. The bus contributes 13%, train 13%, bicycle 2%, and walking 17%. Thus, 40% of the trips are made by alternative means of transport. As for the purposes, it is observed that 35% of the movements are made for commuting to work, while a notable share also gathers for recreation travels (21%) (see Figure 2). The departure times of trips included in this cluster appear at the morning and afternoon peak hours, as can be observed in Figure 3. Specifically, at least 75% of the commutes of this group take place from 7:00 to 11:00 in the morning and from 13:00 to 19:00, when is the peak of this cluster. It turns out that the start times of 50% of the trips in the second cluster correspond approximately to those not covered by the first cluster. Additionally, it is evident in Figure 4 that the trip distances of the second cluster are similar to those of the first cluster. Indeed, they range between 1000 and 6000 m. In fact, 75% of the reported are less than 5 km long. Figure 2: Percentage of trips included in each cluster vs. (**a**) selected transport mode and (**b**) trip purpose. The third cluster consists of 121 trips (8.98%). Regarding the mode of transport, this cluster is characterized by trip that are 45% served by metro, tram or suburban railway (see Figure 2). Additionally, 14% of the trips are conducted using buses. So, around 60% of the trips are carried out using Public Transport. Of course, the remaining 30% of trips are made by cars (private cars or taxis). In this group, commuting to work accounts for 22% and recreation for 16%. The trip departure time in the third cluster, for around 75% of the trips, range between 7:00 and 10:00 and 16:00 to 20:00. Regarding the distance of the trips, 50% of the observations show distances between 5 and 10 km, as can be observed in Figure 4.  
The fourth cluster consists of 383 trips (28.43%).