This research was conducted in October 2018 in Rangsang Subdistrict Waters, Meranti Islands Regency, Riau Province, to determine change in coastline occurred in the coastal area of Rangsang Subdistrict in the last 20 years, and to analyze the effect of shoreline changes on Indonesia's territorial sea area in the district of Rangsang, Meranti Islands Regency, Riau Province. Results of show that …