Zonal editing must (generally) start with an external .ufm file which, once the mapping of old zones into new has been fully defined, is copied into the appropriate cells of the new internal matrix. It is, however, also possible to edit the internal matrix “in situ”, in which case the program automatically copies the internal matrix into temporary external .ufm file, from whence it is recopied/edited into the new internal matrix.
Thus, with respect to the original zone definitions on the input .ufm file, the new matrix may:
1) delete old zones (in both rows and columns);
2) create totally new zones (whose sequential position is determined by their “name”);
3) compress the existing zones into larger zones (i.e. aggregate or add zones together);
4) rename existing zones (and therefore potentially change their sequential position);
5) split (i.e. disaggregate) and/or copy old zones into new zones
In greater detail these five sets of fundamental operations may be described as follows:
1) Deletion is straightforward - both the row and the column corresponding to a single selected zone are removed. Alternatively a range of zones, e.g. all external zones, may be removed.
2) New zones are added in the rows/columns corresponding to the sequential position of the new zone numbers. The cell values to be inserted in these elements may be either defined uniformly by row and column (e.g. set all row elements to 1 and all column elements to 2) or they may be copied (and/or factored) from an existing zone’s row and column cells. Thus you may create a new zone in a trip matrix which “looks like” an existing zone or, under “copy”, the new elements may be the sum of multiple zones, an average of multiple zones or a weighted sum of multiple zones. Alternatively, the cell values in the new rows and/or columns may be set either (a) from an external data source via the “update options” described in Section 10.5.1.2, (b) via matrix manipulation equations (to selected rows/columns, 10.8.2) described in 10.8.1 or (c) by screen editing (10.10.4).
3) Compression aggregates two or more existing zones (i.e. rows and columns) into a single larger zone (“many to one”) by adding cell elements together whereas renaming basically copies one zone into another with a different name (“one to one”). Since compression is essentially similar to that of defining sectors to be aggregates of zones it may sometimes be more convenient to perform this step via sector definition; for example, with sectors it is possible to view both the zonal and the sectoral matrices within the same run.
4) The zones to be compressed may either be in a block of sequential zone numbers (e.g. zones 4, 5, 6 and 7) or “mixed” (e.g. zones 1, 5, 7 and 8). They may either be aggregated into a zone with a completely new number (e.g. zones 4 to 7 go into zone 40) or an existing zone (e.g. zones 4 to 7 all go into zone 4, in which case the original zone 4 effectively stays where it was).
Renaming is straight forward - the row and column elements are moved to the new sequential positions. In effect “renaming” is an alternative form of compression, the difference being that with renaming a single zone is converted into another single zone; with compression several zones are converted into one. Renaming and compression are therefore included within the same menu structure with the first two (many into one) being effectively compression and the next two (one into one) being effectively renaming.
5) The “Split” function may be used to divide a single zone into a set of 2 or more sub-zones with separate factors by row and column. Normally at the end of the process the old zone has been deleted. However the new sub-zones may in fact contain the original zone number, so that this function effectively duplicates renaming - split a zone 100% into a different zone - and copying - split a zone 100% into itself and 100% into the new zone. Use whichever seems most convenient. Note that certain options plus factors leave the total number of elements in the matrix unchanged so that these operations are suitable for matrices such as trip matrices but probably not for matrices such as distance matrices where, if a block of zones were to be aggregated together, one would wish to average the cell elements, not add them together. Thus if you wanted to aggregate four zones from a trip matrix choose factors of 1.0; if it were a distance matrix choose 0.25.
To a large extent the above functions mirror those available under “M5” (see Section 10.16.3) and as a distinct batch file MXM5 (see 10.20.20) which dump the internal matrix to an output .ufm file. Thus to aggregate a matrix from zones into, say, “districts” one could either aggregate on input (as here) and produce a new .ufm by simple output, or else read in the zonal matrix and aggregate to districts on output. One difference is that the input options use only interactive input commands whereas the outputs use control files. (Although through the use of key files both can be run equally well in a purely batch mode.)
From version 10.7 it is possible to save the instructions input interactively (e.g., which zones to copy, which to delete, etc.) in the form of a “control file” as required by the MXM5 procedure; see 10.20.20 and Appendix W.3.