I have read many reviews that says Google map is much better than Apple map. This is not true in Thailand! Google map is terrible for Thailand. There are so many mistakes and editing or mapmaker is not allowed here. Whereas Apple map is quite accurate. Nostra map is also very good for Thailand but it doesn't have turn-by-turn voice guidance.

Did you mean in entire Thailand or just in a single city?

I haven't actually tried it through out the whole country. But it works really well in Bangkok and vicinity, Huahin, Phuket and Nakornrachasima.

It isn't so bad in the UK either. It's by no means perfect, and there are some noticeable mistakes, but it's definitely not as bad as many claim.