Options 4 through 8 are based on simpler forms of zonal transformation – either a pure compression/aggregation from zones to “groups” or, conversely, a pure expansion from groups to zones. They follow the basic principles described in Section 10.4.4 and 10.4.5 and effectively perform the same functions but with outputs directly to an external .ufm file as opposed to the internal matrix.
Thus option 4 and 5 aggregate zones into groups defined either (option 4) via an input .Z2G file, or (option 5) using a pre-defined zone-group mapping as “carried” by the .ufm file or as previously introduced within this particular run of MX. For example the .Z2G file might have been set by the parameter FILZ2G during the matrix build (see Table 10.1 in section 10.5.2) and the necessary information stored in the .ufm file.
Option 6 aggregates zones to groups using a hierarchical set of rules based on zone numbers plus parameters IROCKY and NBASE (see 10.4.4) while option 7 aggregates zones to sectors following the current definitions of sectors.
Finally option 8 – first introduced in release 11.2.9 – outputs a compressed or aggregated matrix but following a specific set of rules within the TfL SATURN zone naming conventions; see 5.1.7.2. Thus the output matrix is aggregated into a traffic borough to traffic borough format. Note that in order to make use of this option the internal matrix must be recognised as a TfL-based matrix, most easily done by toggling option 16 within Main Menu 1 (10.1.1.1) although it is also possible to declare a matrix as a TfL matrix at the point of its creation (see the parameter TFL in Table 10.1 in 10.5.2).