swamp, wetlands, muddy fields, (kokuji)
垈 centers on low, waterlogged land: a swamp, wetlands, or muddy fields. It is a kokuji created in Japan to describe such terrain.
垈 is a Japanese kokuji, combining 代 (replace, substitute) and 土 (earth, soil) to represent a type of land—swampy or muddy fields. The exact reasoning behind the component choice is uncertain, but it likely relates to land that is not solid ground.
The top 代 suggests something that is not the real thing, and the bottom 土 is earth. Picture land that pretends to be solid but is actually a muddy swamp: 垈 is wetlands.
For タイ, imagine a swamp so thick it feels like a tie-dye of mud and water: tie -> タイ, and the muddy fields are a messy tie-dye pattern.