Identification items (i.e., ID items) are those data items that uniquely identify the questionnaire and define hierarchical levels. They are usually geographic items, such as Province, District, or Enumeration Area, or other unique identification, such as Survey ID Number. These data will appear on every record in a data file, as they are "common" to all of the records. The maximum number of ID items is fifteen.
If you are using absolute mode, you will typically want to structure your dictionary so that the ID items begin in column 2; in this way they will precede a record's data items (column 1 is usually reserved for the record type identifier). If you are using relative mode, you have no choice but to place the ID Items first; the system assigns a consecutive position in the order in which the items are created.
For a pictorial representation, open a dictionary in CSPro and press Ctrl+L (L=layout). Press Ctrl+L again to toggle this view off.