Thanks for clarifying. So the following complaint about DPI does not make sense, given that a 50 inches wide screen with a resolution of 600 pixels per inch has 32000 pixels.
OK, I've gone and read the OP's text rather than just the quoted part. It seems he's talking about combining multiple X screens into one logical coordinate space, like I expect one or more of the existing extensions do, e.g. Xinerama.