Ppi is a print parameter, it's irrelevant until the image hits paper. A pixel is just a pixel, but on paper that pixel needs to have a physical size, which is what ppi defines. Ppi is metadata that can be arbitrarily changed at any time without affecting the image data.
On screen there is already a screen pixel grid, so it's just a question of mapping image pixels to screen pixels. A 1:1 mapping, aka 100%, is always the most accurate. So again, ppi is wholly irrelevant.