In this study, we intensively characterize the structure of nitrogen-doped reduced graphene oxide (NrGO), focusing on the carbon defects to elucidate its electrical conductivity. To do so, we intentionally selected three different NrGO materials, which were prepared by different representative synthesis methods, namely, hydrothermal, high-temperature-assisted, and mild reaction methods. All of the materials had different functional group distributions in terms of oxygen and nitrogen, as confirmed by X-ray photoelectron spectroscopy. Interestingly, infrared spectra indicate that the materials exhibit similar carbon defect distributions associated with oxygen and nitrogen functional groups, albeit with different defect concentrations. The NrGO materials differ significantly in terms of their graphitic sp2 carbon lattices, as characterized using various techniques, including near-edge X-ray absorption fine spectroscopy, Raman spectroscopy, and powder X-ray diffraction. Our investigations revealed that detailing the structure of the sp2 ring cluster is key to understanding the electron-transfer properties of the NrGO materials. Furthermore, an interesting linear relationship was found between the logarithm of electrical conductivity and the aromaticity of the NrGO materials, providing a new versatile and simple tool for the design of conjugated carbon materials with similar functional groups for carbon-based electrical conductivity, as the reported NrGO materials.