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The IrTe transition metal dichalcogenide undergoes a series of structural and electronic phase transitions when doped with Pt. The nature of each phase and the mechanism of the phase transitions have attracted much attention. In this paper, we report scanning tunneling microscopy and spectroscopy studies of Pt-doped IrTe with varied Pt contents. In pure IrTe, we find that the ground state has a 1/6 superstructure, and the electronic structure is inconsistent with Fermi surface nesting-induced charge density wave order. Upon Pt doping, the crystal structure changes to a 1/5 superstructure and then to a quasi-periodic hexagonal phase. First-principles calculations show that the superstructures and electronic structures are determined by the global chemical strain and local impurity states that can be tuned systematically by Pt doping. [ABSTRACT FROM AUTHOR]