A new method for mapping the plasma operational space of a tokamak reactor is proposed. The operational space within poloidal field (PF) coil engineering constraints is defined by three parameters, ψ, βp, and Ip, which are the magnetic flux supplied by the PF coil system, the poloidal beta, and the plasma current, respectively. It is also shown that the boundaries of the plasma operational space have a one-to-one correspondence with the PF coils. The design specifications of the PF coil system are thus related to the plasma operational space.