The following two maps are most respected over the years. 

1. The Arbor Foundation Map. (Last map produced in 2006)

2. USDA Map. (Last map produced in 1990)

“The newest 2006 map reflects that many areas have become warmer since 1990 when the last USDA hardiness zone map was published. Significant portions of many states have shifted at least one full hardiness zone.

This warming is great  news for those that are looking to grow palms in areas that was too cold in the past.

In response to requests for up-to-date information, the Arbor Day Foundation developed the new zones based on the most recent 15 years’ data available from the National Oceanic and Atmospheric Administration’s 5,000 National Climatic Data Center cooperative stations across the United States. Hardiness zones are based on average annual low temperatures using 10 degree increments. 

Hardiness Zone Map by the Arbor Day Foundation