I guess I thought they were more like distinct biomes but it really is just uniform chunks of temperature range. I also didn’t know that they were defined by the US Department of Agriculture, who created the first such system to help gardeners. There are similar maps for Australia, Canada, and parts of Europe, but no single global system. What’s your zone?
I’m in USDA zone 5a, and zone 5b is mere miles south of me. While it’s not a perfect system, I have been using it, along with reading from the horticultural societies at the local universities, as a guide for what plants will most likely survive the winters here.
Yeah my zoning is somewhat borderline too. I try to think of it as a high level guideline. And then for fine tuning I pay attention to what I see in other people’s yards, and try to talk locally about what works/ doesn’t. Our local buy nothing group is pretty good about donating extra starts or even extra yield.