This study analysed the greater Seoul area (GSA) in terms of naturalness, a representative indicator of natural scenic beauty, and created an assessment map, shifting from a traditional urban development perspective to a landscape perspective. It also developed a “normalised naturalness index” by combining the results of the expert metric score with the Hemeroby index, which was used as a naturalness assessment representative item. Then, it interpreted the naturalness status of the GSA landscape characteristics. As a result, the landscape of the GSA demonstrates the following five characteristics: First, the central business districts in the capital city of Seoul are densely developed areas with a very high degree of human intervention. Second, the satellite cities built to solve Seoul’s housing and logistics problems are rated as “a little less, but still heavily humanised” as a landscape characteristic. These areas are becoming increasingly humanised. Also, it is worth noting that the third characteristic, regarding moderate landscape areas, has a distinctly different meaning for areas outside of the city boundary, as well as those within the city boundary. Although these areas are in the same statistical category, they have two different meanings: one is the area where the average values converged on “moderate” by virtue of urban forests near the city centre, and the other is the area outside of Seoul that has a Hemeroby value of 0.5–0.6, which refers to open spaces such as agricultural lands, wetlands, or coastal areas. Fourth, suburban forests are reserved with legal restrictions to curb excessive urban sprawl, as well as parts of the demilitarised zone along the border areas of North and South Koreas. The last landscape characteristic is illustrated in the scenic area of the eastern woodlands. The normalised landscape naturalness index developed through this study provides an overall understanding of the environmental state of the GSA. Future research may build on the results of this study to refine methods for assessing public perceptions of naturalness.