@turquoise-- I think doctors differentiate them based on their appearance because all warts are caused by HPV. So the same treatment options are available for treating all warts, regardless of which type they are.
If you want to find out if you have plane warts, just compare pictures of different warts to see which one your warts resemble the most. Plan warts are much smaller than regular warts and they are much darker in color, they are usually red or brown. Regular warts tend to be bigger, irregularly shaped and the same color as the skin.
Some people think that plane warts are completely flat, but that's not true. It will be a little raised, it won't be completely even on the skin. It's just the very top of the wart won't grow out into irregular shapes, it will be flat.