• Main USDA Page
• USDA Hardiness Zones
• How USDA Maps Created
• How Map was Started
• Basic Map  Requirements
• Why New USDA Hardiness Map

The average annual minimum temperature data were analyzed for Mexico, the United States, and Canada.  Of 14,500 stations that measured temperature during the period of interest, almost 8,000 could be identified by latitude and longitude and by a valid average annual minimum temperatures (i.e., an average based on at least 10 years of data).  Data from only the latter stations were sued in the map.  The data were archived by Servicio meteorological Nacional (Tucubaya, D. F., Mexico), the National Climatic Data Center (Asheville, NC), and Environment Canada - Canadian Climate Centre (Downsville, Ontario).  The map is an Albers Equal Area Projection.  Standard parallels of 29.5º and 45.5º were sued to generate the map of the three countries.  The map was computer generated by latitude and longitude.  Because of the large area involved, it is not possible to draw one map that is accurate for all of North America.  The part representing the United States has the least distortion.  The Agricultural Research Service proposes to periodically evaluate weather data and issue updated maps as necessary and appropriate.

© Notice: All information on this and related pages is directly from the USDA Agricultural Research Service, Miscellaneous Publication Number 1475 "USDA Plant Hardiness Zone Map".  This publication is not copyrighted, and permission to reproduce all or any part of it is not required.