Difference ppi with dpi ?

before us to the DPI, we discuss the pixel

PIXEL: An element of the picture and the smallest representation of a point in a graphic image.

example: G2 screen has a 1920 x 1080 = 2.073.600pixel with a width of 5.2 so = 424 ppi
pixel density it is SHARPNESS PICTURE function of DPI in android is scaleable (zoom)

 Starting from (ldpi) low-density 120 dpi up> (xxxhdpi) extra extra extra high-density 640dpi
 LG G2's default 480dpi = xxhdpi

 if we use the DPI under it - with a pixel density of 424

* + resolution pixel density will not change (image sharpness) Android means we think the screen as it is more widely (let's say phablet / tablet) because Android can not detect the physical size of the screen width we DPI reference so he was the one reference to display screen.
while we remain in FullHD resolution.

 theory simply this:
let's just reduce the dpi = zoom out
 it adds dpi = zoom in