*1.3. Classification of Vertiport-Related Topics*

Reading through the 49 scientific publications extracted from *Scopus* as explained in Section 1.2, we identified eleven topics which will be proposed as a classification of the current vertiport research. The topics and their prominence across those 49 publications are displayed in Figure 5. The sizes of the rectangles correspond to the weight of each topic. The larger the area of a topic the more attention it received so far. The weight of a topic was determined via weighted sum analysis. First, for each publication it was analyzed if the topic played no role (0 points), a minor role (1 point), or a major role (2 points). This was applied for all topics giving each publication a sum of points. Second, the amount of points for the topic was divided by the sum of all points of that particular publication to create a normalized point-score (so that the sum of point-scores for each publication is 1). Third, the normalized point-scores of the topic were added up across all publications.

**Figure 5.** Classification of vertiport-related topics and their weight in the reviewed scientific literature (49 publications); size of rectangle corresponds to prominence of the topic.
