identifies one or more
variables in the map and response data sets that define a map area.
This argument is used only when map and response data sets are specified.
Every variable that
is listed in the ID statement must appear in both the map and response
data sets. The variable identified by the
id-variable(s) argument
can be of type numeric or character and should have the same name,
type, and length in both the response and map data sets.