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?
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.