The example 'east of the library' gives the relative location of a place.
Explanation:
A relative location of the place is the one which is described with a reference to a nearby landmark.
The landmark serves as a place of common prominence for all the nearby locations.
For example, when a place is said to be located at a certain point to the west of the Empire States Building, the Empire States Building is the landmark of reference.
The location of the place is relative to this reference landmark and is thus called 'relative location'.