By default, iMovie displays video in the Project browser in multiple rows. This view lets you see more clips in a single window, but it requires you to scroll vertically through longer projects. In this view, video clips often break across two rows. This break is represented by jagged edges on the right side of one row and on the left side of the next row down.
iMovie lets you view projects horizontally as well, which means that the entire project is laid out in a single row (single-row view). To see the entire project, it’s necessary to scroll horizontally, but clips are never broken. Therefore, it can be easier to see the project’s progression. Single-row view also makes it easier to view and manipulate other project elements, such as sound clips and titles.
To display projects horizontally:
Click the Horizontal Display button in the upper-right corner of the Project browser.
To see more of the horizontal display, click the Swap button in the iMovie toolbar to exchange the placement of the Project browser and the Event browser.
After you click the Horizontal Display button, all other projects open in horizontal orientation until you switch back to the default view by clicking the button again.