Vineyards may be scored to assess their suitability for producing good-quality wine grapes. The most famous system is that used in the douro valley of northern Portugal for port production. Vineyards are allocated points, from plus 1,680 for the most promising, to minus 3,340 for the least favoured, taking into account yield, soil type, mesoclimate, vineyard maintenance, grape composition, encépagement, and vine age. Highly classified vineyards are entitled to produce as much wine as they are able each year, while the production from lower classifications can be restricted to meet demand. The champagne region of north east France has a similar, if considerably less precise, system whereby whole communes are given a percentage rating, between 80 and 100.