In this talk, we study the correspondence of the connection and the metric depending on the well-defined duality between 2-dimensional almost-Riemannian structures and coherent tangent bundles of rank 2. Moreover, we analyse their dependence on the local coordinate and try to construct a “pseudo-inverse” of the metric. Furthermore, we try to study the Gauss-Bonnet type theorems for generic 2-dimensional almost-Riemannian manifolds with boundary.