The P1 line represents where the penumbra begins to be visible at moonset. The U1 line represents where the umbra begins to be visible at moonset. Between those two lines people can see only the penumbral phase. The U4 line represents where the umbral phase ends at moonset, and the P4 line where the penumbral phase ends at moonset. West of the P4 line people can see the entire eclipse...but of course it is only a partial eclipse.
OK, you answered my question a minute before I posted it.