a.制圖信息為統(tǒng)計(jì)單元的離散數(shù)據(jù) b.數(shù)據(jù)應(yīng)符合比率量表的處理,并表現(xiàn)為相對(duì)數(shù)值 c.以顯示數(shù)值的差異