For the four super-classes, B-E, the changes in (a) resolution, (b) half-map 3D FSC sphericity, and (c) map-to-model 3D FSC sphericity are plotted with respect to the dataset from untilted images and as a function of tilt angle (see Supplementary Figures 7, 8, 9, 10 for all raw data). Map densities of (d) beta sheets and (e) alpha helices from reconstructions at various tilts for class E are also shown to illustrate the effects of change in resolution and resolution anisotropy (the two are interrelated). Beta sheets are from uL22 and the alpha helices are from uL29. Side chain densities are marked by red asterisks, while beta sheet separation is indicated by a green arrow. The direction of preferred orientation is indicated by the red double-headed arrow. As expected, map isotropy steadily improves with increasing angular tilt, which also affects global resolution and can accordingly facilitate interpretation of structural features. For example, smearing of beta-strands (d) and alpha-helices (e) parallel to the direction of preferred orientation is ameliorated with tilts, which can be especially important at borderline resolutions for interpreting atomic models.