Chapter 6: User Interfaces for Mobile Media 267 the details become too small and the acceptability of content is decreased. A set of images can form a slideshow, where the images are dis- played in a specifi c order. The slideshow is usually based on images that the user chooses, but also metadata-based relations can be used to create a dynamic slideshow based on the selected attributes. The slideshow either uses playback controls, which means that the user can move between images manually (transition to the next or previous image in the set), or the transition is automatically based on a pre-set time interval. Above, we mentioned a slideshow in relation to playback, however viewing a single image requires different kinds of controls, including those for navigating between the images in a set of images, and chang- ing the orientation. Rotating an image is easy when the device is handheld, but if an external device is used, a fast method (a fi nger gesture or keypad shortcut, for instance) to rotate an image 90 degrees clockwise or counter clockwise is a necessity. In mobile devices, visual content often needs to be scaled down to make it fi t the screen. In this process, some details are lost because the number of visible pixels is less than the actual number of pixels. In order to view the details, the user must zoom in, which implies that the whole image is not visible anymore. To see the parts outside the current view, the user must be able to pan (scrolling) the view. There are mechanisms (such as earlier mentioned MiniMap) that can aid in scrolling the view. Essentially, zooming may be used with any visual content, although it is less frequently used with temporal content. This is because during the playback the user cannot be sure if something relevant has been clipped due to the zoom. Maps are a special case of images. Even though some users enjoy viewing maps as such, they are often used for way-fi nding or locating tasks. A technical difference between most “normal” images and maps is that while most images, photos included, are bitmaps, maps are often vector graphics that enable a smooth change of zoom level. Wayfi nd- ing requires the user to enter the start and end points (sometimes also other waypoints) for the route, which is then automatically calculated. The waypoints are pre-defi ned points of interest, selected locations on the map, or addresses. Furthermore, the preferred route is usually weighted based on points of interest, scenery, distance, or travel time. It is straightforward to overlay the route on a map image, which makes it easy to see the progress as well as anticipate events and places ahead. It is benefi cial to change the zoom level to see either more details of environment, or a wider overview. Especially in car