DateLens: A Fisheye Calendar Interface
for PDAs
BENJAMIN B. BEDERSON and AARON CLAMAGE
University of Maryland
and
MARY P. CZERWINSKI and GEORGE G. ROBERTSON
Microsoft Research Calendar applications for small handheld devices are growing in popularity. This led us to develop
DateLens, a novel calendar interface for PDAs designed to support complex tasks. It uses a fisheye
representation coupled with compact overviews to give the big picture in a small space. The interface also gives users control over the visible time period, as well as supporting integrated search to
discover patterns and outliers. Designed with device scalability in mind, DateLens currently runs
on desktop computers as well as PDAs. Two user studies were conducted to examine the viability
of DateLens as a replacement for traditional calendar visualizations. In the first study, non-PDA
users performed complex tasks significantly faster with DateLens than with the Microsoft Pocket
PC 2002TM calendar (using a PDA emulator). In addition, they rated DateLens as being easier
to use than the default calendar application for a majority of the tasks. In the second study, the
participants were expert Pocket PC users and the software was run on their own devices. Again,
DateLens performed significantly faster for the complex tasks, and there were satisfaction differences favoring each calendar for different kinds of tasks. From these studies, it is clear that
DateLens is superior for more complex tasks such as those associated with longer time periods.
For daily event tracking, users familiar with the default Pocket PC calendar strongly preferred its
daily view and behaviors.
Categories and Subject Descriptors: H.5.2 [Information Interfaces and Presentation]: User
Interfaces—Graphical user interfaces (GUI), Interaction styles, screen design; I.3.6 [Computer
Graphics]: Methodology and Techniques—Interaction techniques
General Terms: Design, Experimentation, Human Factors
Additional Key Words and Phrases: Fisheye distortion interfaces, information visualization, calendar interfaces, PDAs, animation, graphics The portion of this work performed at the University of Maryland was funded in part by a generous
gift from Microsoft Research.
Authors’ addresses: B. B. Bederson and A. Clamage, Human-Computer Interaction Laboratory,
Computer Science Department, Institute for Advanced Computer Studies, University of Maryland,
College Park, MD 20742; email: {bedrson,aclamage}@cs.umd.edu; M. P. Czerwinski and G. G.
Robertson, Mircrosoft Research, one Mircrosoft Way, Redmond, WA 98052; email: {marycz,ggr}@
microsoft.com.
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C 2004 ACM 1073-0616/04/0300-0090 $5.00
ACM Transactions on Computer-Human Interaction, Vol. 11, No. 1, March 2004, Pages 90–119. DateLens: A Fisheye Calendar Interface for PDAs • 91 1. INTRODUCTION
More and more people carry small Personal Digital Assistants (PDAs) with
them to help manage day-to-day information. While these devices can be helpful
for retrieving relevant information when it is needed, our informal polling of
colleagues tells us that they are less helpful for more complex tasks, such as
those involving larger time spans. This is not surprising since these devices have
limited screen space, forcing users to jump around through multiple screens,
making it harder to relate disparate pieces of information.
We designed DateLens,1 a new calendar interface for PDAs, to better support
these more complex tasks such as picking a good weekend to go camping, counting the number of Mondays in November, finding the start and end dates of a
trip. These are instances of tasks that we classify more generally as scheduling,
navigating and counting, and searching, respectively.
Our secondary goal was to design a calendar interface that would scale down
to smaller devices such as mobile phones, and up to larger devices such as
desktop displays. This is important since individuals are likely to access their
calendar information from these and other devices. Offering a single interface
across devices would give users a consistent experience, and, eventually, the
ability to more readily switch between devices using whichever one is more
accessible.
The DateLens design addresses these goals by using a fisheye distortion
technique coupled with carefully designed visualizations and interactions appropriate for a pen-based device and a small display [Bederson et al. 2003].
Figure 1 shows DateLens running on a Pocket PC device.
The basic approach used by DateLens is to start with an overview of a
large time period using a graphical representation of each day’s activities.
Tapping on any day expands the area representing that day, and reveals the
list of appointments in context. Users may change focus days, zoom in further for a full day view, search for appointments, and reconfigure the viewable
space.
This interface shows varying time span displays within the same framework using animated transitions between view changes, and thus, may improve
users’ ability to maintain a sense of where they are. This paper describes the
interface along with the results of two user studies comparing DateLens to
the standard Microsoft Pocket PC 2002TM calendar interface. Evidence from
these studies supports our hypothesis and provides many useful ideas for improving the DateLens user interface design.
1.1 Related Work
Fisheye distortion techniques, initially called bifocal displays, were introduced
by Spence and Apperly [1982] 20 years ago. At that time, the basic concept was
to distort the information space so focus items were enlarged while peripheral
items were shrunk. A few years later, Furnas [1986] generalized this approach
by suggesting a “degree-of-interest” function, which calculates the relevance of
1 DateLens is available for download at www.cs.umd.edu/hcil/datelens.
ACM Transactions on Computer-Human Interaction, Vol. 11, No. 1, March 2004. Fig. 1. The DateLens interface with the view configured to show 12 weeks and consecutive levels of detail as the view is: a) shown as an overview; b)
zoomed into one day; c) focused on that day; and d) zoomed into an appointment. All transitions between views are animated. 92
• B. B. Bederson et al. ACM Transactions on Computer-Human Interaction, Vol. 11, No. 1, March 2004. DateLens: A Fisheye Calendar Interface for PDAs • 93 each item in the information space. This result is then used to calculate the
size and visibility of that item.
Fisheye distortion techniques have been applied to a number of domains,
from graphs [Sarkar and Brown 1992] to trees [Lamping et al. 1995] to
menus [Bederson 2000], among others. Their effectiveness has been mixed,
but in at least some cases, such as hierarchically clustered networks .[Schaffer
et al. 1997], fisheye interfaces have been shown to benefit users. The common theme has been that fisheye views are appropriate when users need
to see details of some specific items in the context of a large information
space.
The idea of using fisheye distortion to view calendars is not new. It was first
suggested over ten years ago by Furnas [1991], where he described a textual
Lisp-based calendar program. We followed the basic approach Furnas created
at that time. A tabular display shows days in the calendar, and clicking on individual days causes the amount of space allocated to that day to be increased.
Furnas’ calendar used varying amounts of space to show different days, so that
the focus day was largest, and other days were sized in inverse proportion to
the distance from the focus day (although days in the past were always tiny
because the assumption was that users were more interested in the future.)
This program, while impressive for its time, did not support graphical representations of appointments, animation, searching, or full screen views, and did
not have an interface to control which and how many weeks to display. It was
not designed with small displays in mind. In addition, it was not evaluated
with users, and was not pursued past the publication of the above-mentioned
technical report.
Fisheye visualizations have also been used successfully to view and interact
with generic tabular information. The best known example of this is probably
Table Lens, which presents an interface for tabular data [Rao and Card 1994].
This visualization approach was designed for tables with many rows, but a
modest number of columns. It represents each cell with a horizontal bar whose
length is proportional to the value of the cell for numerical data, and whose
position represents categorical data. The height of each row is scaled to fit the
available space. Users may then focus on individual or multiple cells (or rows
or columns). In addition, users can sort rows to help see relationships within
the data. While this approach is somewhat similar to the present work in that
it uses a fisheye distortion to view tabular data, it is not directly applicable to
calendar information as it is designed for spreadsheet style information that
has one item per cell, rather than the multiple and possibly conflicting appointments of calendars. In addition, it does not support the searching or navigation
that calendar users require. Nevertheless, the acceptance of this technique (as
demonstrated by its successful commercialization [Inxight 2003]) gives hope
that users will be able to understand and navigate calendar information in a
tabular format using a fisheye view.
Researchers have also developed other techniques to visualize and interact with calendar information. Plaisant and Shneiderman [1992] were among
the first to develop small visual representations of calendar information.
Mackinlay et al. [1994] developed a 3D “spiral calendar” visualization. This
ACM Transactions on Computer-Human Interaction, Vol. 11, No. 1, March 2004. 94 • B. B. Bederson et al. approach, while not suitable for small devices since it displays several visual
representations simultaneously, does have a fisheye-like quality in that it displays detailed appointment information with visual links back to larger scale
calendars. So, users can see what week an appointment comes from, what
month that week is in, what year that month is in, and so forth.
Perhaps surprisingly, fisheye techniques have rarely been used for interfaces
for PDAs and other devices with small displays. One use was by Bj¨ork et al.
[1999] who used “flip zooming” to display web pages and then personal information including calendar data [Bj¨ork et al. 2000] on a PDA as demonstrated
within their PowerView application. Flip zooming consists of presenting one
medium-sized focus page and several tiny pages in the periphery that can be
used for navigation. At a high level, the basic approach of flip zooming is similar
to DateLens. However, DateLens differs from flip zooming in that flip zooming is designed to support hierarchical textual data while DateLens supports
tabular data with a natural visual abstraction. Furthermore, flip zooming has
system-defined viewpoints while DateLens allows users to define views. Finally,
DateLens adds two important new features: integrated search and animated
transitions.
2. DATELENS
DateLens is the fisheye calendar interface we designed for use primarily on a
PDA (Figure 1). It was designed and built at the University of Maryland and
Microsoft Research then joined the project to run the experiments. DateLens
runs on both Pocket PC devices as well as on full-sized Windows machines.
As described in the related work section, DateLens draws its design from
a range of earlier work. While the individual features of DateLens represent
variations of existing approaches, our primary contribution is the integration
of a host of techniques to create a novel application that is both usable and
useful in an important domain. In addition, we present two studies that show
how this design works in comparison to a more traditional calendar design for
small devices. We hope that DateLens illustrates how existing techniques can
be applied in new ways to new domains, and in doing so, advance the state of
the art.
DateLens was built to target currently available devices running the
Microsoft Pocket PC operating system. These devices are small enough to fit
comfortably in a hand, have high quality 240 × 320 pixel screens, and fast
enough processors to support modest animation.
Since DateLens was designed for a pen-based PDA, we have been careful
to design the interaction so that it requires minimal text entry and simple
interaction. The entire interface can be accessed with single taps, although
dragging offers some modest extra features—including access to tool-tips and
fast scrollbar usage.
The rest of this section describes the DateLens interface in detail, including a
description of its navigation capabilities, the visualizations that represent calendar information at different sizes, and how search capabilities are integrated
into the interface.
ACM Transactions on Computer-Human Interaction, Vol. 11, No. 1, March 2004. DateLens: A Fisheye Calendar Interface for PDAs • 95 2.1 Navigation
A fundamental characteristic of DateLens is its ability to support users in easily
customizing their view of the calendar. Most commercial calendar applications
provide mechanisms to directly switch between day, week, month, and year
views, and to change which range of dates are visible with each view. However,
the different views are disconnected and inflexible. One goal of DateLens was
to offer the same functionality in terms of a range of views, but to do so in an
integrated and flexible fashion. Using animation and fisheye distortion, users
can see the relationship between the range of dates they are viewing and the
previous view. As such, users should not have to expend as much mental effort
to manage context and figure out “where they are.”
The basic organization of the display is tabular (Figure 1). Each row represents one week, with columns representing the days of the week. The number of
visible rows can be changed from one, representing a single week, to 52, representing an entire year. When a day is tapped, the view is gradually changed to
expand the day that was tapped on (Figure 1a, 1b). This and all view transitions
are animated over a user-defined period that defaults to about 250 milliseconds.
The animations are rendered by linearly interpolating the position of each grid
line for the in-between frames. The result is that each view smoothly transitions
from one view to the next.
The view can be changed through direct manipulation by interacting with
the calendar itself, by manipulating widgets in the periphery of the display, or
by using special hardware button shortcuts. One of the challenges was to make
it extremely easy to configure the view. The final design only uses interaction
mechanisms that most users are familiar with, including tapping on an item
that they want more information about, and manipulating familiar buttons and
widgets.
Direct Manipulation. DateLens was designed to take advantage of user
familiarity with clicking on hyperlinks to find more detailed information about
the item they clicked on. It allows users to tap anywhere on a day to focus on
that day, minimizing other days (Figure 1a).
Within a focused day (Figure 1b), users can tap on the background, or tap
on the maximize button to zoom in to a full day view. Or, users can tap on the
minimize button to go back to original view with no days focused.
Within the full day view (Figure 1c), users can tap on an appointments
background or the appointment’s maximize button to view the appointment
details. Tapping on the day’s minimize button returns to the original view, and
tapping on the overlapping-windows button returns to the focus day view.
Within the full appointment view (Figure 1d), scrolling shows the full contents of the appointment. Tapping on the minimize button returns to the full
day view.
2.1.1 Peripheral Widgets. The “range slider” widget on the right side of the
display controls how many weeks are visible at a time. It acts like a traditional
scrollbar, but the thumb has two additional buttons that are used to manually
set the start and end dates of the current view. The view dynamically changes as
ACM Transactions on Computer-Human Interaction, Vol. 11, No. 1, March 2004. 96 • B. B. Bederson et al. Fig. 2. A series of views as the bottom of the scrollbar thumb is dragged downwards to show:
a) 1 week; b) 1 month; c) and 3 months. Fig. 3. The views resulting from a) unchecking the weekend checkbox; and b) leaving just weekends
in March checked. the scrollbar is manipulated, but for animation efficiency, appointments within
days are only shown when the scrollbar is released. Figure 2 shows a range of
views as controlled by the range slider.
Another way to configure the space is to manipulate checkboxes on the top
and left sides of the display. These checkboxes specify whether space gets allocated fully to the correlated set of items, or if those items are minimized. The
left side of the display has one checkbox for each month. The top side of the display has one checkbox for weekdays and one checkbox for weekends. Figure 3
shows the result of two different configurations of checkboxes.
There is also a “home” button in the top-left corner of the display that resets
all navigation settings to a user-configurable state.
2.1.2 Hardware Buttons. On desktop computers, graphical user interfaces typically offer keyboard shortcuts so that expert users can quickly
ACM Transactions on Computer-Human Interaction, Vol. 11, No. 1, March 2004. DateLens: A Fisheye Calendar Interface for PDAs • 97 access commonly used functions. On PDAs, there is no keyboard, but
there are special hardware buttons that applications can use for a similar
purpose.
When DateLens runs a Pocket PC device, the “calendar” button can be used
to cycle between the preset views of one day, one week, one month, and three
months. The “joystick” (a small 4-way rocker switch) offers motion in four directions, and we use that to move the “active” day, which is indicated to the user
by a dark blue highlight. Pressing the center of the joystick focuses on that day
(or maximizes it if it was already focused). The joystick can also be used when
a day is focused or maximized. On a desktop PC, the keyboard can be used to
navigate through the calendar by using the arrow keys to change dates, the
enter key to zoom in, the escape key to zoom out, and the space bar to switch
between preset views.
2.2 Visual Representations
A crucial aspect of the design of DateLens is the visual representation of the
calendar for different configurations. We decided to use a “semantic zooming”
approach that we developed from our prior work with Zoomable User Interfaces
[Bederson et al. 2000]. Semantic zooming means that objects are visually represented differently depending on how much space is available to display them.
Using this technique, there are no explicit view modes. Rather, the fisheye distortion algorithms first allocate space, then each cell renders itself using a view
that is appropriate to the available space. The graphical views are scaled to
fit the available space, while the textual views use a constant-sized font, and
the text is wrapped to fit in the available space.
The four available views are:
r Tiny View. This shows a graphical representation of the day’s appointments.
It includes depictions of all-day appointments with a white rectangle at the
top of the day rectangle. It uses color to represent different appointment
types, and depicts appointment conflicts using multiple columns. The pen can
be dragged across appointments to show tool tips with textual information
about the appointment under the pen. In large-scale views, where each row
is thinner than a threshold, the black lines separating rows are removed to
make the display less “heavy” (Figure 1a).
r Agenda View. This shows a textual list of appointments in order by time.
There are actually two representations in this view. If there is a smaller
amount of space available, a smaller font is used, and the appointment times
are not listed. If there is more space available, a larger font is used, and the
appointment times are listed (Figure 1b).
r Full Day View. This shows a traditional full day view with a schedule of the
entire day, and appointments positioned at the appropriate times. It shows
all-day appointments and conflicting appointments, and uses color in the
same way as the tiny view (Figure 1c).
r Appointment Detail. Traditional widgets are used to show the details of a
particular appointment (Figure 1d).
ACM Transactions on Computer-Human Interaction, Vol. 11, No. 1, March 2004. 98 • B. B. Bederson et al. The decision of which view to show is, by default, made by DateLens depending on how much space is available in a given cell. There is a threshold cell size
for each view that determines what to display.
While the initial design of DateLens was motivated by small displays, one
of the attractions of its design is that it scales nicely to larger displays as well.
Since the decision of which representation to use is made based on how much
space is available for a particular cell, the same layout algorithm and rendering
code works on larger displays as well. Figure 4 shows DateLens running on a
desktop PC at 1400 × 1050 resolution.
2.3 Search
The last primary component of DateLens is search. Search is important because
it lets users identify patterns and outliers within a large time span. When users
search in DateLens, the days that contain an appointment matching the search
criteria are highlighted. The highlights are maintained while users continue
to operate DateLens normally so the space can be explored to understand the
results of the search.
In addition to highlighting the visible days within the current view, “attribute
mapped scrollbars” [Hill and Hollan, 1994] show which days are highlighted in
both the past and future (Figure 5). The scrollbar shows indicators representing
which days are highlighted within and outside of the current view. This mapping
of search results to the scrollbar is fixed to this single attribute, and is not under
user control.
While it is natural to support searching for arbitrary user-entered text
strings, that is somewhat problematic because it is notoriously difficult and
slow to enter text on PDAs. So, while DateLens supports free text search, it
also provides two search mechanisms that do not require text entry: pre-built
searches and searches based on existing appointments.
2.3.1 Free Text Search. To search manually, users enter text in the text
box at the top of the display. A somewhat tricky issue is how to deal with
search strings that consist of multiple words. Should the search consist of the
conjunction or disjunction of the words, or the actual search string? No one
of those approaches worked for all of the experimental tasks in our studies.
Instead, DateLens operates like many current Web search engines, using a
simulated “vector” based search [Baeza-Yates and Ribeiro-Neto, 1999, pp. 27–
30].
Vector searches work by using a number of characteristics of the search to
rank the order in which the results are shown. This results in an ordering that
usually matches user expectations. Exact string matches are typically listed
first, conjunctions (where all the words match) are listed next, and disjunctions
(where not all the words match) are listed last.
DateLens is a little different since it does not present an ordered list of search
results, but instead highlights whichever days match. Rather than ordering
search results, DateLens only presents highly ranked search results. It works
by first performing an exact string match, and if there are any results, they alone
ACM Transactions on Computer-Human Interaction, Vol. 11, No. 1, March 2004. Fig. 4. DateLens scaled up to 1400 × 1050 pixels on a desktop computer. There is room to display an entire week with the full day representation, even
while showing three months of the calendar. DateLens: A Fisheye Calendar Interface for PDAs
• 99 ACM Transactions on Computer-Human Interaction, Vol. 11, No. 1, March 2004. 100 • B. B. Bederso...

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