<p>Data video is an increasingly popular genre of narrative visualization. To distill a data story into a video, designers need to draft a sequence of data facts and visually connect them by animated transitions. Such animated transitions are critical for illustrating data changes and enhancing narrative coherence; however, their design still lacks systematic guidance. To fill this gap, we developed a design space by collecting and analyzing 89 high-quality data videos. The design space characterizes the design of animated transitions under three dimensions: narrative relation, data change, and transition animation. We conducted an online design workshop with 14 participants to evaluate the effectiveness of our design space on designing transitions. The results show that the design patterns summarized in our design space can be used to efficiently guide the transition designs in data videos.</p> Graphical abstract <p></p>