This derived field contains a code for the patient's county (first two characters) and local authority district (last two characters) of residence. It is derived from the patient's postcode in the field homeadd.

This field is used in conjunction with currward (current electoral ward) to produce a unique value indicating the ward within a given district where the patient resided (ie because identical Currward codes are allocated to many local authority districts, currward is meaningless in isolation).

If the patient is resident within a Unitary Authority, the first two characters will be 00 (zero, zero) and the local authority component may not be useable.

4an = Local authority code

S = Scotland

U = England (NOS)

W = Wales

Y = Not known

Z = Northern Ireland

X = Foreign (from 1991 onwards)

9999 = Not known