GIS helps but it cannot make decisions or meaning. Geography is important. Maps and data can be manipulated to say almost anything. And then these maps and classifications become data sources for other GIS work. Best to include original data when possible.
Classifications vary according to each factor.
There may be a cause for the grouping which may lead to understanding the environment better. Leads to other problems and answers. Land classification depends on the type of features that are to be grouped. There are separate classifications for soil, landuse, vegetation, geology, etc. However, a feature's category depends on the method of classification used.