  We explore the fine structure of the holographic entanglement entropy
proposal (the Ryu-Takayanagi formula) in AdS$_3$/CFT$_{2}$. With the guidance
from the boundary and bulk modular flows we find a natural slicing of the
entanglement wedge with the modular planes, which are co-dimension one bulk
surfaces tangent to the modular flow everywhere. This gives an one-to-one
correspondence between the points on the boundary interval $\mathcal{A}$ and
the points on the Ryu-Takayanagi (RT) surface $\mathcal{E}_{\mathcal{A}}$. In
the same sense an arbitrary subinterval $\mathcal{A}_2$ of $\mathcal{A}$ will
correspond to a subinterval $\mathcal{E}_2$ of $\mathcal{E}_{\mathcal{A}}$.
This fine correspondence indicates that the length of $\mathcal{E}_2$ captures
the contribution $s_{\mathcal{A}}(\mathcal{A}_2)$ from $\mathcal{A}_2$ to the
entanglement entropy $S_{\mathcal{A}}$, hence gives the contour function for
entanglement entropy. Furthermore we propose that
$s_{\mathcal{A}}(\mathcal{A}_2)$ in general can be written as a simple linear
combination of entanglement entropies of single intervals inside $\mathcal{A}$.
This proposal passes several non-trivial tests.
