GMS and Analyzer are both capable of filtering report by interface so you can see, for example, only traffic from a particular subnet to the Internet. This custom report can be saved and scheduled to be sent daily / weekly / monthly as well. See the following articlefor some examples how to filter and save custom report:
VLAN Interfaces typically are as follows: X8:V100, X0:V20. However, on GMS and Analyzer, when VLAN interface info is sent in the syslogs, the character “:” is replaced with “-“. So, you will need to use values such as X8-V100, X0-V20 in the Reports filters.