Sectors play a very traditional role within SATURN and have fairly restricted properties. They represent a very high level of zonal aggregation as described in section 5.1.7 such that the maximum number of zones is 20 (or, strictly 21 since sector 0 is regarded as a valid sector number unlike nodes, zones, groups etc.) Sectors are common to both matrices and networks.
Like the alphanumeric zone names sector definitions may be obtained “externally” from either:
an associated GIS file (see Block 8, App. Z),
a network .ufs file (see 6.8),
an explicit “zone-to-sector” (.Z2S) file (10.2.5.5 below),
“hierarchy” rules based on either TfL conventions or by a parameter IROCKY (see 5.1.7 and Table 10.1 in 10.5.2 below), or
alternatively, set within MX using a sub-option of the Files menu.
Generally speaking the number of sectors should be small enough that the entire sector-to-sector matrix may be viewed within a single screen or page so that an intuitive “feel” for the matrix may be obtained. Looking at individual cells in, say, a 200 x 200 matrix provides very little useful information.
Most options within MX may be applied either at the basic zone-to-zone cell level or - provided that sectors have been defined - at the sector-to-sector level.
At present only one set of sector definitions is allowable within MX at any one time, i.e. multiple “groups” are not allowed. They could however be handled, somewhat awkwardly, by creating more than one GIS file which defines the sectors (10.3.3) and swapping between them.