Options 9 and 10, introduced in 11.2.6, allow an “aggregated” matrix (e.g., a matrix which has been defined at the level of, say, group-to-group cells) to be expanded (“disaggregated”) into a matrix of “zone-to-zone” cells where the relationship between “groups” and “zones” may either by set by a .Z2G file or – preferably - via the existing zone-group mappings. Note that, in this case, the zone-to-group mapping is used “in reverse” in order to define which zones are within each group.
We note that under expansion the value in an individual group-to-group cell is copied into each and every corresponding zone-to-zone cell so that the sum of all the zone-to-zone cells will be considerably greater than the sum of the group-to-group cells. Hence this option is not suitable for a matrix of “quantities” such as a trip matrix whereas it would be suitable for a “qualitative” matrix of, say, group-to-group distances or group-to-group factors.
N.B. The use of the terms “group” and “zone” above is purely nominal, they are simply referring to two different levels of (spatial) aggregation. The same procedures could equally well be used to transform a matrix defined in terms of “boroughs” into one defined by “districts” or from “boroughs” into “zones”, etc. etc. See Section 10.2.5 for a discussion on different levels of aggregation and their “names”.