Anywhere you travel through the wine country, you will notice that the wineries often mention the particular appellation or approved viticultural area (AVA) where it resides. A Viticultural Area is defined by the Alcohol and Tobacco Tax and Trade Bureau (TTB) after a review of, among other things the climate, geography, and soil of the defined area. On their website, the TTB states the following: “A Viticultural area is a delimited grape-growing region distinguishable by geographical features, the boundaries of which have been recognized by the TTB.”
A listing of Approved Viticultural Areas can be found at the following website address: https://www.ttb.gov/wine/ava-map-explorer.
The website states that the Viticultural area may extend across political boundaries, and there is no maximum or minimum size. Additionally, the entire area should possess a unifying feature that distinguishes it from neighboring areas. All of that can be boiled down to the understanding that the growing conditions are distinctly different between appellations, with each area favoring certain types of grapes.