This article proposes an innovative approach based on analyzing a raster map in geographic information system to perform substation expansion planning for a very large-scale real network. This approach provides an irregular planning miniregion to decompose the planning area into irregular miniregions to tackle such a very large-scale real network expansion planning. Meanwhile, the article develops a suitable model regarding the concept of a system of systems to bring about collaborative interactions between miniregions to preserve the integrity of the distribution network. This model has been established using the proposed index called the maximum permissible radius of load feeding. Computer simulation is performed for a very large-scale subtransmission system of Mashhad, consisting of 1 359 410 consumers spread in an area of 11 450 km2, to demonstrate the efficiency of the proposed methodology.