To avoid future complications, the boundary between neighbours should be properly defined.

Answer: Option B

Limited : restricted in size, amount, or extent; few, small, or short.
Demarcated : set the boundaries or limits of.
Explained : make (an idea or situation) clear to someone by describing it in more detail or revealing relevant facts.
Interpreted : explain the meaning of (information or actions).
Defined : mark out the boundary or limits of.

Synonym of Defined is Demarcated