I'm using Photoshop Elements 4, so maybe this doesn't apply to later versions.
Why, when I go to create a new image in Photoshop Elements, does it insist on a dpi (dots per inch) setting?
Digital images don't have a size, they just have a number of pixels vertically and horizontally, so you can't specify the number of dots per inch - it depends on the device that is displaying/printing/projecting the image.
Just think of a projector displaying a 600 by 800 pixel image - shine it on a surface just a few inches away and the image could measure 6 inches by 8 inches - 100 dots per inch. But move the projector further away and the image could be 60 inches by 80 inches - now it's only 10 dots per inch - but the digital image itself has not changed!
So digital images don't have size dimensions - only pixels.
So why does Photoshop Elements keep talking about dpi?