Revision with unchanged content. Due to continuous advances in mobile hardware, devices such as smartphones and personal digital assistants (PDAs) are becoming a truly mobile alternative to bulky and heavy notebooks, allowing the users to access and search remote data while on the road. Application fields that benefit from increased staff mobility are business consultants, mechanical engineers, and doctors in hospitals, for instance. However, a drawback that impedes this development is that the form factor of mobile devices requires a small- sized screen. Hence, given a large data set, only a fraction of it can be displayed. To identify important data the users typically have to linearly navigate the off-screen space via scrolling. For large information spaces, this is tedious, error- prone, and particularly slow. In contrast, the concept of zoomable user interfaces (ZUIs) has been found to improve the user performance for many retrieval and exploration scenarios. While ZUIs have been investigated mainly in desktop environments, this work analyzes the usability potentials of zooming and panning in a mobile context given the constraints of a small screen and pen-input.