Explain the Modularity of Object oriented analysis

Modularity is closely attached to encapsulation; you may think of it as a way of mapping encapsulated abstractions into physical, real modules. It is a feature of a system which has been decomposed into cohesive and loosely coupled modules. 

Cohesion and coupling provides two goals for defining modules. A module should be make cohesive (shared data structures and similar classes) with an interface that allows for minimal inter-module coupling.

It is very important to remember that the decisions regarding modularity are more physical issues, on the other hand the encapsulation of abstractions is logical issues of design.