Opportunistic spectrum access creates the opening of under-utilized portions of the licensed spectrum for reuse, provided that the transmissions of secondary radios do not cause harmful interference to primary users. Therefore, it is important to characterize the effect of cognitive network interference due to such secondary spectrum reuse. In this paper, we show how a new statistical model for aggregate interference of a cognitive network, which accounts for the sensing procedure, secondary spatial reuse protocol, and environment-dependent conditions such as path loss, shadowing, and channel fading can be used to assess the aggregate interference in specific environments. Specifically, we consider scenarios like power controlled primary network, secondary network with interference avoidance mechanism, and non-circular coverage region.