Every province has a seal (ตราประจำจังหวัด), a circular graphic with some typical things of the province depicted. These are relatively often seen in Thailand, for example on the websites of the provinces, or also on the big street signs welcoming the drivers when entering a province. However I was quite surprised when I first saw the Flags of the World website talking about flags of the provinces (ธงประจำจังหวัด). These flags usually feature the same provincial symbol as depicted the seal, together with some colors which have some connection with the province. Depicted is the flag of Surat Thani province.
In Thailand almost every public place is cluttered with either the Thai national flag, a flag with the symbol of the King, or around temples a flag with the Buddhist wheel. But I never ever saw any of these provincial flags, not even at the province hall. Also the book "Thong Thai Laem 1" by Chawingam Macharoen I bought once does not mention them, just many other flags used in Thailand. The only official place I have seen these flags so far are PDF files with province profiles from the Ministry of Interior. But the flags in those are of so low resolution it hardly possible to make out the actual contents. The best renderings available on the web were at vexilla-mundi.com, however right now the section on the Thai provinces is "under construction". So this flag of Surat Thani I tried to create to match those low-resolution pictures, it is probably not fully correct with its aspect ratio, the colors or the size of that chedi in Chaiya in relation to the whole flag.