The Scope field determines the scope of the options data. RFC 3954, Cisco Systems NetFlow Services Export Version 9 clearly explains it and the information it contains:
Scope 1 Field Type
The relevant portion of the Exporter/NetFlow process to which the Options Template Record refers.
Currently defined values are:
3 Line Card
For example, the NetFlow process can be implemented on a per- interface basis, so if the Options Template Record were reporting on how the NetFlow process is configured, the Scope for the report would be 2 (interface). The associated interface ID would then be carried in the associated Options Data FlowSet. The Scope can be limited further by listing multiple scopes that all must match at the same time. Note that the Scope fields always precede the Option fields.
You define the scope type, then you fill in the Scope data with relevant information related to the scope. The example above from the RFC is telling you that if you set the scope to be an interface, then you put the interface ID in the scope data. You would then report on the data for that interface.