The network-of-zones concept provides a simplified basis for constructing mixing models appropriate to tomography. For miscible single-phase mixing in three-dimensions, of the order of 104 volume elements (voxels) are needed to interpret mixing results from 16 element electrical resistance tomographic (ERT) sensing rings stacked axially. Experimental mixing and dispersion in passive scalar pulse tests can be acquired at video frame rates by ERT and simulated by integration of sets of first-order ordinary differential equations. Non-uniformities in gas hold-up and solids suspension can also be detected and quantified in three-dimensions by resistance tomography. Modelling the approximately axisymmetric mixing of these two-phase examples can be achieved by a much smaller number of algebraic equations. Tomographic modelling provides new insights into the fundamentals of mixing in a stirred vessel. The reduced computational requirements of networks-of-zones make real-time model-based control more feasible.