Around a month ago, @gung suggested to make nominal×113 a synonym of categorical-data×1987 because they are "literally synonyms". This has initially gotten some support, until @ttnphns objected on the grounds that ordinal-data×531 is also "categorical": nominal and ordinal, he says, are two sub-types of categorical data, and therefore we should leave all three tags separate. The whole discussion is here in the comments: https://stats.meta.stackexchange.com/a/4717/28666.
I feel that we need to arrive to some decision here.
Option #1 (@gung): map nominal to categorical-data. To be consistent, this would require looking through
categorical-datathreads and moving the ones about ordinal data to ordinal-data. A quick search
[categorical-data] ordinal is:questionyields 166 Qs, and not all of them would need to be retagged, so we are probably talking about minority of questions, perhaps ~100.
In either case we will need to edit the wikis and wiki excerpts to clarify the usage. At the moment some information there is conflicting, e.g. wiki for categorical-data says
categorical values are considered as abstract entities without any mathematical structure such as an order or a topology [written by @whuber in 2012]
but its wiki excerpt says
Some people consider ordinal scale categorical too [written by @ttnphns in 2013]