I hope to find you well, I am emailing you from Dublin, Ireland. We are a software company named VR Retail, we are a new start up and we are concentrating on our first product www.vrhomeandgarden.com. In essence we are a virtual reality suite of design planners for the home and garden. We are launching our first product, VR Gardens this November in the UK but are looking to then launch it in the states and we are looking for some helpful advice on the categorization of the U.S regarding climate and growing of plants. We would love for you and your organisation to help us.

Hope to hear from you.

Gary

No need to re-invent the wheel here, Gary. There are two sources I can think of that you should look at for this purpose:

The US Dept. of Agriculture has their plant hardiness zone maps. They aren't all that useful for gardeners as they were intended for farmers to use. But growers of nursery plants for home gardeners use their hardiness zones as a beginner reference.
http://www.planthardiness.ars....

Sunset Magazine came up with a much better, more informative map for gardeners:
http://www.sunset.com/garden/c...

No need to leave this site to use the USDA zone map.
http://garden.org/nga/zipzone/

The Sunset Zones are very detailed for the USA, and one design goal was that, within any one Sunset Zone, and all throughout that zone, similar plants will thrive.

However, I must admit that I'm not a "planning" gardener. I like to try to do things and see what I can get to grow.

Are you familiar with the international Koppen climate system? They have the same goal, but they cover the world. Hence each Koppen zone is broader than any Sunset zone.

https://en.wikipedia.org/wiki/...
http://people.eng.unimelb.edu....

maps: http://www.hydrol-earth-syst-s...

Google image maps: https://www.google.com/search?...

exact Koppen Zones in each US COUNTY:
http://koeppen-geiger.vu-wien....

the zones shown in the map are very broad; maybe some combination of Koppen and USDA/Sunset.
Example- it seems I'm in the same green Koppen zone as most of Texas and Florida

I agree, Koppen has very broad categories.

But it lets you compare Milwaukee with Milan!