By the virtue of the Town and City Planning Act the government has issued zoning regulations for Samui (see map below giving the type of use to which land and property may be put in specific areas). The restrictions and the requirements for utilization of land in each zone is different. The main aim is to set rules for sustainable development of Samui and protect Samui's environment.
Sample document local zone regulations under the Town and City Planning Act (details missing)
1 -  Low density residential area |
7 -  Kept open for the public use |
2 -  Medium density residential area |
8 -  Reserved forest area |
3 -  High density residential area |
9 -  Educational area |
4 -  Industrial and warehouse area |
10-  Tourist and fishery |
5 -  Specific agricultural area |
11-  Religious area |
6 -  Agriculture area |
12-  Government offices and public utilities |
Among the list of prohibited uses under the City Planning Act is for largest part of the island land allotment for any purpose, except for agricultural purposes (read warning for buyers of land). Land allocation for residential purposes is prohibited. It is allowed in this area to build a single house but property development is not allowed. Large areas of the island does not have any form of title deed and therefore it is not allowed to build and restricted for private use. In addition large of the island are protected under other environmental laws. In Samui large areas of land have been upgraded illegally (often with the help of local officials) and ownership papers have been illegally issued or title deeds have been issued that include forest land - read articles 'land scam stopped in time', or 'Ilegal land deals', ministers not involved in land scam, investors invade 100 plots of land to name a few samples.
Still you see large plots of land for sale by the Samui real estate agents, hill side, hill top land, great views, investment opportunity, etc., suggesting subdivision for property development is possible, though, the land could be classified as forest land (dubious titles) or has an agricultural purpose only!
Related: Buying building a house in Thailand - sample building regulation for Samui, land allocation reg.
