o Samui is in the Gulf of Thailand, about 35 km northeast of Surat Thani town (9°N, 100°E). It is the most significant island in the Chumphon Archipelago. The island measures some 25 km at its widest point. It is surrounded by about sixty other islands, which together compose the Ang Thong Marine National Park (Mu Ko Ang Thong National Park) and include many other popular tourist destinations, including, Ko Pha Ngan, Ko Tao, and Ko Nang Yuan.
The central part of the island is an almost uninhabitable tropical jungle mountain called Khao Pom, peaking at 635 m. The various lowland and coastal areas are connected by a single 51 km road, running mostly along the coastline and encircling the bulk of the island. On the northwest coast of the island is the old capital, Nathon. Although Nathon spreads over a large area, the actual port and main business district is relatively small.
Nathon is the major port for vehicular and goods transportation from the mainland, it is the centre of the fishing industry, and remains the seat of the regional government. The majority of governmental functions are based here, as is the public hospital. Being the location of the main port and the closest inhabited area to the mainland provided the impetus for Nathon becoming the commercial centre for Samui locals. More recently, the decline in dependence on the local coconut industry, the continued growth and development of the tourist industry, and the northeastern location of the airport, has seen the slow move of the commercial centre to Chaweng.