Well, one of the principal methods which is used to help separate the two figures and keep the fact of their actual unity a secret is the living arrangements of both of them. Note how Dr. Jekyll lives in a wealthy and opulent home. The laboratory, however, is described as "a certain sinister block of building." The laboratory is neglected and dilapidated, and it is therefore symbolically fitting that it is Mr. Hyde that is seen entering and exiting from this establishment, and that Dr. Jekyll enters and exists from his home. Yet, as the novel makes clear, these two rooms are actually connected, even though both buildings appear to be on two different streets. The labyrinthine layout of the roads in this area makes it impossible to discern that these two separate structures are actually part of one building. This makes the concealing of the identity of Mr. Hyde a lot easier, as he can leave through the laboratory, which is taken by all to be for all intents and purposes as a separate building.
Of course, the connection between these two buildings is symbolic of the connection between Dr. Jekyll and Mr. Hyde, and the evil side that all of us possess, no matter how detached we look as if we are from such sordid connections.