TIL that the USDA hardiness zones are each a ten-degree band of average minimum temperature in the fahrenheit scale, and the “a” and “b” suffixes break each zone down further into 5 degree ranges.

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?