The values stored in this table indicate the isolation block to which each individual main in the network belongs. This table provides the entry point for the calculation of any main isolation solution. The relationship between mains and blocks is strictly 1:1; that is, each main will only be associated with a single block. The number of records in Table 1 will be equal to the number of main features in the network. Additionally, Table 1 must document the unique GISOBJID (i.e. the value of the GISID field in the EAM equipment record) for each main feature represented in the user’s GIS network.