Illustration of different subsets of the grid nodes used to calculate the correlation coefficients between model and target maps. (a) Atomic model (blue sticks) superposed with partially interpreted target map (gray); the correlation coefficient CCbox between the target and model map is calculated over the whole cell. (b) Molecular mask calculated by Jiang & Brünger (1994), CCmask. (c, d) Mask derived from atomic images at higher and lower resolutions, CCimage. (e, f) Peaks within the given volume in higher and lower resolution model maps CCvolume. (g) Mask derived from the peaks of the model (blue) and target (magenta) maps, CCpeaks; the total mask is the union of the blue and magenta masks.