1. IIRC raster graphics is like MS paint and shit. Usually referred to as Bitmap. The program renders the photo block by block or something.
Vector graphics is like Inkscape or Adobe Illustrator. The picture is continuously rendered regardless of size/stretching/skewing.
If you got Adobe/Macromedia Fireworks play around with the Bitmap and Vector subsections on the left pane.www.spatialdesign.info/blog/134/files/2009/01/vectorbitmapexample.png
2. So you can fucking edit the layers individually rather than saving it as a flattened image. Saving in jpeg flattens/merges all layers into a giant cluster so if you wanna edit out like a shadow on the topmost layer you can't unless you save it as a .psd file.
3. im pretty sure its picas.
4. No. That only gives the pixels per inch. thats like saying two monitors are the same size cause they both got 800x600 resolution.(kinda skeptical on this one)
Do the rest im too lazy.