How the USDA Zones map works:
Figure out what your USDA Zones Number is by matching the color of the area you live with the chart on the right.
Plants across the site and other sites across the web will sometimes show what Zones a plant will grow well in.
The main thing this map takes into account is the harshness of the winter.
Many plants can be grown nearly anywhere for a summer but will not survive the winter in harsh locations.
Credit for the image goes to the USDA.
For an interactive map that lets you zoom in on a particular state you can see it on the USDA site HERE.