Integrative model building with ArpNavigator. Assessing the quality of initial electron density by building helices (a) or skeletons (b). Following model building, in the case of bound ligands the binding site can be identified (c) and the coarsely placed ligand refined into the map (d). Solvent molecules can be modelled (e). Contour levels are at 1.5σ in (a) and (b) and at 3.5σ in (c) and (d). The resolution of the maps used is 3.2 Å in (a) and 1.9 Å in (b), (c) and (d); all maps shown are 2mFo − DFc maps.