Consider a more detailed model, where for example you might wish to capture separate districts within a city. One tempting approach would be to nest one template (for a district), together with its related variants, within another (for the city as a whole). However, the resulting structure would be extremely rigid, and not hugely practical, as different numbers of variants may be required in each sub-group; in this example, different numbers of districts within each separate city.
Figure 1: Inflexible nested template structure
Note: Nested templates are not currently allowed.
Generally it will be more flexible to have separate replications for each district, using collections to group these by city.
Figure 2: Flexible flat structure