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After reading Jef Raskin’s The Humane Interface it seems that ZUIs are a obvious paradigm choice to make easier interfaces. Apparently the original iPhone interface was a big investment in that direction with many ZUI patterns, although not considered 100% a ZUI.
Why are ZUIs not a popular UI paradigm / more common?
I too have been asking myself this question ever since I read The Humane Interface. Although Jef Raskin laid out his ZoomWorld as a complete idea, the real ZUI expert is Ben Bederson. He has been building and studying zooming interfaces for decades. He also has some of his own answers to your question. He summarized, ‘manual organization of information in a zooming environment rarely makes sense’. He wrote an entire paper on the question, ‘The Promise of Zoomable User Interfaces’. From the section ‘Why ZUIs Are Challenging’ (pp 5–6):
As summarized in Table 1, the potential benefits of ZUIs are sometimes mirages. ZUIs are generally engaging (although they make some people feel physically sick) and visually rich. But the promise of simplicity falls short.
While human visual perception does make it easy to see where one is navigating, the reality is that it places a heavy load on short term memory to remember where in space you just were and where things are. And the requirement of human memory to know how space is organized means that ZUIs don’t scale up very well. ZUIs are often motivated by the physical world and how people like laying papers out on their desk. But no one wants all of their papers on their desk. It is much more common to have only a relatively small number of papers that are actually being worked with.
The visual overviews that ZUIs offer for free by zooming out may seem like a solution to the load on human memory, but in practice it doesn’t because visual overviews of any complexity require significant scanning and visual search in order to find anything. If there are just a small number of objects, then the visual search task is not hard – but of course, for a small number of objects, you don’t need a ZUI to solve your organizational problems.
Finally, the visual richness of ZUIs is a double-edged sword. It requires skill to design a complex space with documents of arbitrary size, aspect ratio and color that people can comprehend and scan. Also, people are not as good at scanning 2D designs as 1D layouts – unless the layout is highly structured. But highly structured 2D layouts don’t work well for visual objects of arbitrary aspect ratios. Designers are obligated to leave a lot of unused space, scale down the large objects so they are unreadable, or crop the large objects – thus losing much of their distinguishability.
I’d like to add a few points of my own. First, Jef Raskin’s zoomable interface makes the most sense in a document/object-centric context. Application-centric environments are conceptually at odds with such interfaces. Raskin’s ZUI is good for organizing large amounts of information in a way that makes applications obsolete; but the current computing landscape is all about “apps” (following Apple’s lead, from the original Macintosh to the iPhone). Even the iOS home screen, a kind of minor zoomable interface (especially after nested folders were added), is restricted to organizing app icons, not real content.
Second, paradigm shifts tend to take a long time. Concepts like graphical interfaces and direct manipulation were invented in the ’60s, but it took until the mid-’80s for these paradigms to be available to the general public. The Internet and hyperlinked documents took even longer. Multitouch screens go back to the ’80s, but the iPhone was the first generally-available affordable implementation. Zoomable interfaces are often more resource-intensive; by the time they were practical, traditional GUIs were quite established.
I believe a “killer app” is necessary in order to facilitate this app-centric–to–object-centric paradigm shift. In my opinion, the best way to answer why ZUIs aren’t more popular is by negating the premiss: build one! (That’s my own plan.)
I think there is room for ZUIs and most of maps UIs use ZUI pretty well. The challenge is to apply ZUI to more generic apps.
However, I believe that there are some constraints when you design a Zoomable interface:
As a side note I'm building a library called Zircle UI that borrows some ZUI ideas.
As a preface to this answer, please note that I can only infer (as I'm speaking on behalf of a lot of designer/programmer that I've never met)
conjecture: programmers are lazy
explanation: in code, it is easier to isolate sections of an interface. it keeps code clean, and files short, with limit dependencies. in order to have a zooming interface, the zoomed in interface could need to be tightly coupled with the zoomed out interface. this COULD make for some nasty code. (obviously you can code anything, so note the word COULD in all caps). iOS follows this paradigm often with UIViewControllers https://developer.apple.com/reference/uikit/uiviewcontroller/1621380-presentviewcontroller?language=objc In short, it is much easier to barf something onto the screen then it is to code nice animations and transitions
conjecture: zooming interfaces done poorly CAN lose context (and confuse the user)
explanation: if you zoom into too far, or too fast, the user may have a hard time of keeping track of 'where' they are and will feel cognitively heavy
conjecture: zooming interfaces don't fit as many paradigms as buttons do
explanation: when designing an interface, you are thinking about what makes sense. if it makes sense to emphasize going into and out of sections then go for it. Logically, this would make the most sense when you are traversing a hierarchy (animals -> dogs -> types of dogs), or spacial map (earth -> north america), or something that the user naturally associates with depth (like walking or looking closely). You can see how it wouldn't be adding much to Domino pizza's website.. order online -> (zoom) -> chicken, pasta, or pizza -> (zoom) -> pizza etc
conjecture: a zooming interface is slower than just changing the interface
explanation: if you've ever used a product made by an inexperienced designer, you'll remember the frustration the 50th time you press a button and you have to wait for their frustratingly slow animation to finish before changing the screen. animations in interfaces should be (for the most part) perceived, not noticed. <- if you disagree with this statement, feel free to comment with your favorite Power Point transitions (mines the checkerboard wipe :)
