code: def _find_usage_networking_sgs(self):
          
          logger.debug("Getting usage for EC2 VPC resources")
          sgs_per_vpc = defaultdict(int)
          rules_per_sg = defaultdict(int)
          for sg in self.resource_conn.security_groups.all():
              if sg.vpc_id is not None:
                  sgs_per_vpc[sg.vpc_id] += 1
                  rules_per_sg[sg.id] = len(sg.ip_permissions)
          # set usage
          for vpc_id, count in sgs_per_vpc.items():
              self.limits['Security groups per VPC']._add_current_usage(
                  count,
                  aws_type='AWS::EC2::VPC',
                  resource_id=vpc_id,
              )
          for sg_id, count in rules_per_sg.items():
              self.limits['Rules per VPC security group']._add_current_usage(
                  count,
                  aws_type='AWS::EC2::SecurityGroupRule',
                  resource_id=sg_id,
              )
docs: calculate usage for VPC-related things