I'd classify 化 as a simple ideogram (part of group 2, called "indicators" in the article) because it conveys the abstract idea of 'change' by showing one person

I'd classify 化 as a simple ideogram (part of group 2, called "indicators" in the article) because it conveys the abstract idea of 'change' by showing one person upside down from the other. It isn't a compound ("combograph", group 3) to me because it doesn't build upon the meaning of its individual components. However, this is a fuzzy categorization. In the top-level comment I wrote, I listed 三 'three' as an example of an ideogram but it could be argued instead that it is a compound of three separate 一 'one' characters. Then there's the character 廿 'twenty', which consists of two 十 'ten' characters, that is probably better explained as a compound. So at a certain point it all becomes quite subjective.