A common usability myth is that users don't scroll. You need to have everything important above the fold! CX partners has a great article which dispels that myth. They write:
Over the last 6 years weâ€™ve watched over 800 user testing sessions between us and on only 3 occasions have we seen the page fold as a barrier to users getting to the content they want.
One important aspect they point out is that users use the scrollbar to figure out whether they have to scroll:
One of the most common things we see on a heatmap is a strong hotspot over the scrollbar. The scrollbar is used to assess the page length. Users expect to have to scroll.
This becomes a bit of an issue if the device you're designing for doesn't have a visible scrollbar. The most common example for such a device is probably the iPhone. If you're working on UI design for such a device, here are two common ways of showing users that they can scroll.
Temporarily show the scrollbar
If you open your iPhone's iPod application and switch to the "Vidoes" or "Audiobook" tab, you'll see that a scrollbar will quickly show up, and then disappear. This serves as a subtle hint which tells users that there are more items than they can currently see.
Make it obvious that the content doesn't fit on the screen
If the last row of items on the screen is only partially visible, users will recognize that they can scroll. The iPhone's Photo Library application uses a particularly clever version of this: the button bar at the bottom of the screen isn't fully opaque; it allows you to see that there's more content further down.
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