It's a tourist map with the emphasis on shopping. I agree with the postings that say it's useful, but don't rely on it alone. Unfortunately, Chandler's calligraphic excesses sometimes get in the way of simple navigation. She's good for telling you where the shops are, but she'd never get a job with Ordnance Survey.
Buy it in hostels and tourist areas.
Updates
Is this your business?
They seem to have other maps and guides for Thailand and Bangkok as well.