Line art generally requires even higher resolution. This is typically about 2,450PPI or higher. If you enlarge the art, then you must multiply your resolution need by the magnification factor. Beware of scanners that use interpolation instead of actual optical resolution when stating their maximum resolution. Optical resolution is the most important specification, because interpolation just adds additional pixels based on neighboring pixels but captures no additional detail.
Pixel depth describes how many colors or tones each pixel in a bitmap can have.
It's a description of how much information is recorded during the scan. This is the mathematics of PostScript technology. This is the sum of 256 x 256 x 256. Some scanners can record more, and this allows a wider range of shadow details, although just because a given scanner records a higher bit depth, it does not mean it can differentiate more tonal levels if the scanner is of a poor design. PostScript technology will choose the 8 best bits of data regardless of the quantity created by the scanner and will discard the excess.