What is the 'Sunset zone map'?

What is the 'Sunset zone map'?

Tracy DiSabato-Aust (Garden Designer and Author) gives expert video advice on: What is the 'USDA Hardiness Zone Map'?; What is the 'AHS Plant Heat Zone Map'?; What is the 'Sunset zone map'? and more...

That's for 13 of the western states, and it breaks those areas down into 24 different zones. It's a little more accurate, actually, than the USDA zone because it takes into account some of the other climatic factors that are involved there.