The Effect of Zooming Speed in a Zoomable User Interface

Introduction

Zoomable User Interface (ZUI)

Over the past thirty years the desktop or WIMP (Windows, Icons, Menus, Pointer) user interface has made the computer into a tool that allows non-specialists to get a variety of tasks done. In recent years, however, the applications available under this interface have become larger and more unwieldy, taking into themselves more and more marginally related functionality. Any inter-operability between applications must be explicitly designed in.

As a successor to traditional desktop interface, the Zoomable User Interface (ZUI) or sometimes called multi-scale user interface is a relatively new metaphor which can produce an environment that takes advantage of the user's spatial memory to create a more expansive and dynamic working environment, as well as encouraging finer grained applications that automatically inter-operate with various types of data objects and applications.

A Zoomable User Interface uses the metaphor of an infinite two-dimensional plane to represent the user's workspace. The user's view of this workspace can be varied both in position and scale, and the size of the objects in the workspace can be similarly altered. This model creates sufficient space that the user's data objects can all be assigned permanent geographic locations, leading to an advantageous use of human spatial intuition.

Zoomable User Interface was proposed by Bederson and Hollan in 1994[2]. They proposed to use both panning and zooming to navigate through a large information space via direct manipulation. Their claim is that the physics of zoomable interface allows scaling to larger information spaces in a way that the current metaphor of files, menus and windows cannot match. Their belief is that human-computer interfaces can take advantage of the natural human capabilities of spatial cognition, and that zoomable interface is one approach that does so.

In the same paper, they described Pad++, one of the first ZUIs. Pad++ is a zoomable graphical sketchpad that changes the view of what is displayed in the information space by zooming in or out.

Zoomable User Interface research draws attention from more and more researchers. There have been several implementations of Zoomable User Interfaces developed by individuals for research purposes, as well as some commercial ones that have not been widely accessible.

Tabula Rasa[6] is an example ZUI system developed by David Fox in New York University to identify the design elements which are important to ZUI’ viability as a successor to the desktop style of interface.

Jazz[3], developed in the HCI Lab of University of Maryland at College Park, is a general-purpose toolkit that supports applications using zooming object-oriented 2D graphics. It supports zooming, internal cameras, and lenses in a similar style to Pad++, but does so in a general-purpose manner.

Zomit[10] is another generic package for developing zoomable user interface. It is developed in France as part of the Infobiogen’s VisuGene project.

Some interesting applications based on these ZUI toolkit have appeared.

A web browser companion called Domain Tree Browser(DTB) was developed recently in HCI lab of UMCP, which builds a tree structured visual navigation history while browsing the web. The Domain Tree Browser organizes the URLs visited based on the domain name of each URL and shows thumbnails of each page in a zoomable window.

KidPad[9] is a collaborative story authoring tool for children. It provides basic drawing functionality on a zooming canvas that is provided by Jazz.

Based on Zomit package, ZoomMap provides a graphical interface to the genetic data stored in Infobiogen's HuGeMap database which contains Biomedical images and other types of information.

All these research work shows that ZUI has its strong points and it is more suitable than traditional user interface in some application areas.

Design Issues with ZUI and related research work

ZUI is a relatively new type of user interface. It has its own design issues, which are vital to its success[4,7,8].

One issue is that current ZUIs provide insufficient context to the user. After even a short period of navigation users no longer know where they are in the information space and what it is they are looking at. They are “lost in hyperspace”. There has been a study which compares the two strategies, Zoom-Only and Overview-Detail pair, in displaying the patient histories in LifeLine system. The result shows that Overview-Detail strategy is better in terms of the time that user spends in completing search tasks. One reason of the result is that user easily gets lost when using zoom-only.

ZUIs also suffer from an interaction problem. They provide commands that have to be executed repeatedly on a constantly changing view. The mouse and buttons are too limited to provide an interface to all these commands without the use of new interaction techniques. A group of students have conducted an experiment in Pad++ in order to determine which interaction techniques is better. They tested two styles, flying and dragging, using three-button and two-button. The result shows that two button mouse uses significantly lower time to finish tasks than three button mouse. The researchers of the Zomit project proposed a new type of pop-up menu called a control menu to solve the interaction problem.

There were several groups of students in Computer Science Department of UMCP conducted some experiments to address several of the design issues. [1,5]

We address another design isssue in this experiment: the zooming speed. We will discuss this design issue in the following section.

Zooming speed

Zooming speed means the scaling rate per second. For example, if in one second, a line with the original length of 2 is scaled to be have the length of 4, we say the zooming speed is 4/2=2.

Current ZUIs, such as Jazz, use smooth zooming. The zooming speed they use is slow enough that the scale rate between the same objects in two successive frames is very small and users see the objects being scaled smoothly. When the information space is very large, this smooth zooming strategy will take much time for users to zoom from one scene to another and this may result in the increase of users’ frustration and error rates. A fast zooming speed would be preferred in this situation. However, extremely fast zooming speed leads to very short response time. According to the discussion about response time in the book Designing the User Interface [11], if the response time is too short for the task, it will lead to users’ anxiety and error rate. Thus zooming speed becomes an important design issue for ZUI. The goal is to design the zooming speed so that users can easily find what they want and remember the information that they have obtained.

Our hypothesis is that there exists a zooming speed at which both the user performance and the satisfaction rate are good. In our experiment, we use Jazz to measure how different zooming speeds in a zooming interface affect the perception of human and try to get the bounds of the ideal zooming speed scope.

Department of Computer Science: Direct questions and comments to the student editorial team