When I lived in Ipswich, Massachusetts from 1978 to 1990 my USDA Zone was 5b. In 2012 it was updated to Zone 6b and the updated 2023 map keeps Ipswich at Zone 6b.

From a recent NPR app piece:
Recently, the USDA updated its plant hardiness map for the first time in 11 years. If you’re a gardener — and everybody can be a gardener, even on a balcony or a stoop — this is a big deal! The updated map opens up new possibilities for home gardeners, but there are limits. Let’s explore how the map has changed and what this means for your garden.

Link to the NPR map here (scroll down)

For a deeper dive—

Check the USDA website for info on the how to use the maps, map downloads and map creation

Here’s an example of the precision for my zip code, 92107. On Point Loma, a peninsula, there are distinct microclimates with ocean and San Diego Bay influences. This zone map distinguishing USDA Zone 10b (mine) and 11a makes sense to me. Check your zip code. There are also various map overlays you can choose.

Information About How the Map Was Created