kr: p is the resistivity,with is a constant for every material, for example, copper resistivity is 1.8*10^-8 or 1.7*10^-8 (i dont remember :P)
and it has a unit of "Ω.m".

resistance < (resistivity*the length of the conductor)/the area of the conductor
so
R=Pr/A
so its the same thing
the length,the distance traveled,since the length of a conductor is the same distance that the charge will travel,they are the same thing (r or l or e)in the book that i have, its r,in wikipedia,its e.
and im taking about the same thing.
btw they should make a group for physics and things like it,am i right guys?