Problem: In canvases that have more than one item, what is the right way for users to move between and among these items

Rationale: In ZUIs we tackle two problems, the single large image, and the collection of images/items large or small.  It is imperative that there be a sensible way for users to move between these items that neither punishes them for exploring nor easily gets them lost.

Variants:

• Single click on an item, when zoomed out should zoom this item to fit the viewport.  If item is zoomed in, viewport expands to capture more or all of the scene.  This can be made discoverable with a magnifying glass cursor.
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• Double Click on an item to accomodate for the situation where an item is hyperlinked (to external web page or another object on the canvas) as the single click will send the user to another destination Example Ahead. 
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• Use of Left/Right/Up/Down buttons on the edge of the viewer.  Clicking them will navigate to the item in that direction, this is particularly effective in grid layouts though may cause problems in other layouts as it can create "unreachable" items.  In stacks of items this falls down entirely.
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• Predefined viewports can help the user navigate the canvas in a more structured way via a fixed hyperlink menu that links to the viewports or in a predefined sequence of viewports via back-forward buttons. Ahead use this approach and combine structure with exploration by having unique URLs for each viewport. If zooming away from the viewport the user can return to the viewport by simply using the browser back button.
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• Thumbnails of items can be shown on the viewport, providing the viewport is large enough to accommodate them without hindering ability to zoom around the main image. Users can click on the thumbnails to switch the main image. An example of thumbnails can be seen on Magic Touch in full screen mode.