Gardeners use the USDA's Hardiness Zones to identify plants that will thrive in their area. The current USDA map was last updated in 1990. The Arbor Day Foundation used weather station data to update the map to reflect current temperature and frost data. The first map shows the amount of change, the second shows the updated Zone map. Visit the Arbor Day Foundation's site for a flash version that shows the changes, or read the press release.