Let X be a Hausdorff
continuous image of an ordered continuum. Mardešić proved that X has a basis of
open sets with metrizable boundaries. We use T-set approximations to obtain bases
of open sets for X whose boundaries satisfy a variety of conditions. In particular, we
prove that
dimX
=indX =IndX
=max{1,sup{dimY : Y ⊂ X is metrizable and closed}}.