When researching street art in Bangkok, there are plenty of resources available; maps, blogs, guides, etc. that can help you track down the best spots to wander.
My favourite street art resource on Bangkok came from The Occasional Traveller. The map may be a little outdated these days but it is by far the most comprehensive and will give you a good indication of where to head. This guide was all I needed to hunt down all of these great pieces while I was in town.
