Learn in the textbookData Operations and Levels of Measurement
DefinitionA nominal scale (名義尺度) is a scale whose values are used only to distinguish and classify things, with no meaning of size or order.
ExplanationExamples include gender, home region and product category codes. Even when they are written as numbers, those numbers are only labels for telling things apart, like name tags, so adding or averaging them gives nothing meaningful. Meaningful operations include checking whether two values match and counting the entries in each category.
AnalogyThe numbers on station coin lockers tell you which locker is which; locker 10 does not hold twice as much luggage as locker 5.
Memory hookNominal comes from the Latin nomen, meaning name: names can be told apart, but no name is larger than another.