It often happens that, during a zoom, you hit the edge of the work area
while making a selection. Just keep the space bar pressed to switch to the
Hand tool, and you can quickly change the displayed image section.
Aligning Layer Contents
Some areas in Photoshop are hardly ever noticed. This is one of them. If
you activate the Move tool, you’ll see some mysterious symbols to the right
called Align tools, in the option bar next to Auto-Select and the Transform
controls (which are basically equivalent to Free Transform).
Align tools
If you activate just one layer, the Align tools won’t do anything, but if you
select two or more layers by holding the Control/Command key, then you
can align the layer’s contents with these buttons. Choose from options such
as “Align Top Edge” and “Align Vertical Center.”