We study backscattering phenomena during conduction for graphene nanoribbons of μ m lengths, from single vacancy scatterers up to finite defect concentrations. Using ab initio calibrated Hamiltonian models we highlight the importance of confinement and geometry on the shaping of the local density of states around the defects that can lead to important alterations on the transport process, giving rise to impuritylike conduction gaps in the conductance distribution. Within a statistical analysis of finite defect concentration we show that conductance degradation can become very important.