Is GIS a Discipline or an Inter-Discipline?

As a new lecturer, I am attending a Post Graduate Certificate in Learning and Teaching in Higher Education course. Although I'm only in my first year of the course, we were invited recently to attend a seminar held by the second year students, who are looking at curriculum development. As well as the interesting range of topics investigated, what struck me was the fact that all the topics could be directly relevant to research into Geographical Information Science education, in one way or another.

In particular, a discussion about the disciplinarity of Machine Learning struck a chord with me.  To address the disciplinarity issue, my colleague started by showing a diagram of other disciplines he thought related to his field. My version, for GIS, would start with this:

but of course there are many more areas that could be included. A discipline can be defined as "a branch of knowledge, typically one studied in higher education" (http://oxforddictionaries.com/), so certainly GIS is a discipline in that sense, but it would be interesting to find out which other disciplines people feel contribute to GIS?

(Thanks to my fellow students for the concepts)