# What is the standard zooming factor?

I am making a simple graphing widget that will have zooming functionality. I need to decide the zoom factor to use for typical + / - zoom buttons. My intuition is to go with 15%. What zoom factor will jive best with user expectations about zooming in general?

Update: the data being graphed are user-provided, so the widget doesn't know what kind of data are in there.

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I think the answer depends entirely on the context of the data being graphed. – DA01 Feb 23 '12 at 21:49
@DA01 please see question update – ted.strauss Feb 23 '12 at 22:15
Well, there is no 'standard' since its dependent on the content, and since the content is an unknown, I think you're likely going to have to make a guess at it and see how it works. – DA01 Feb 23 '12 at 22:25
Content here means what exactly? The data from which the graphs are built or the type of the graph? If the latter is known we could come up with a better answer. – Viraj Feb 23 '12 at 23:44

From the user point of view, I would like an image to zoom in to its actual size in 4, preferably 3, steps.

25% -> 50% -> 75% -> 100%
20% -> 40% -> 60% -> 80% -> 100%

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For the sake of closing the question, I've awarded the accepted answer to the only one providing a concrete answer. All the answers pointing out that it depends on context are valid, but I still have to decide how to design my widget. – ted.strauss Feb 27 '12 at 21:42
@ted.strauss Tx. Do let us know when you do decide and adopt a method for your design. – Kris Feb 28 '12 at 6:20
i'm going to start with 20-40-60-80-100 and revise after alpha testing, which might not be for a couple months. i'll come back and post a link. – ted.strauss Feb 28 '12 at 16:31

According to me the zoom factor should also correspond to whether any new information is made visible by zooming using that zoom factor. Ie whether its 15% or 30% if nothing new is shown once the user zooms once, the user has to zoom many times to actually get to what he/she wants to see.

Conversely if the zoom is too much the user will lose orientation with respect to the whole graph.

I doubt I have answered your question but do keep these constrains in mind. The zoom factor should depend on these constraints.

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It's only a suggestion, but you might try to implement a system that zooms depending on how long the user pressed the zoom button. I think it would be nice to make the content zoom along with the mouse button. So, as long as the user holds the mouse button/keyboard button pressed, keep zooming smoothly and slowly enough to make sure the user has to ability to release the button in time.

I think the zoom speed should depend on the size of the content. How larger how faster is zooms. But ensure you have a nice maximum zoom speed. This, in combination with the current zoom factor. I would slow down zooming slowly.

It's just an idea. I don't know if it will be cool, but I think it is worth trying it, if this is applicable for your situation.

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There's a downside to this as well. When the user wants to zoom to full size, he may have to wait too long for that, and then wait some more to realize it is the full size. – Kris Feb 25 '12 at 9:34
A double click could make it zoom at 100%. – Martijn Courteaux Feb 25 '12 at 10:41

You may want to use a slider that zooms in when slid to the right/top and out to the left/bottom. This way the user can decide exactly how far they need to zoom in on the graph.

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There is no standard - it depends entirely on what's being displayed.

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How do you know there's no standard? Maps have a set of standard scales, for example. – dnbrv Feb 24 '12 at 16:23
@dnbrv - if you know of a standard zooming factor that suitable for miscellaneous / unspecified data, I'd be really happy to be proven wrong ;) – codeinthehole Feb 24 '12 at 16:58
Not knowing of any is not an authoritative reference. – Kris Feb 25 '12 at 9:32
Sometimes empirical knowledge provides enough to realise that a question cannot possibly be answered. All answers on this page so far, are based upon conjecture. – codeinthehole Feb 25 '12 at 9:56
@Kris, if someone asked you, "what's the standard colour? " what would you tell them? – codeinthehole Feb 25 '12 at 9:59