  In this paper, two sufficient and necessary conditions are given. The first
one characterizes when the boundary path groupoid of a topological graph
without singular vertices has closed interior of its isotropy group bundle, and
the second one characterizes when the path groupoid of a row-finite k-graph
without sources has closed interior of its isotropy group bundle. It follows
that the associated topological graph algebra and the associated k-graph
C*-algebra have Cartan subalgebras due to a result of
Brown-Nagy-Reznikoff-Sims-Williams.
