You can find that if you scroll down the article far enough, or at https://ahsgardening.org/about-us/news-press/cool_timeline/heat-zone-map-developed/ https://a

You can find that if you scroll down the article far enough, or at https://ahsgardening.org/about-us/news-press/cool_timeline/heat-zone-map-developed/ https://ahsgardening.org/about-us/news-press/cool_timeline/h... - it's based on the number of days above 86 degrees F (30 degrees C). I would like to see these two maps overlaid on each other somehow.