overlay as a core GIS concept is not so strong in humanities GIS

The overlay of different information was one of the very first concepts of GIS. Like the core function, the corner stone, the first brick <...> that engaged the development of GIS on which all GIS users stand now. And it remains one of the most popularly used method for data analysis.

This concept is explained in every basic GIS cookbook, more objectively I haven't encountered any book that would not talk about overlay presenting it as a concept, technique, procedure, method. It's always presented in a very simple way by visualizing or explaining boolean operations. What else could be said? Apart from scale, resolution, data uncertainty problematics probably not much more, until we look into the GIS for Humanities (as Standford coins) and GIS concepts start to sway..

GIS concept suitability for social or humanitarian research is well presented in a book "The Spatial Humanities" writen by geographers, historians at the same time having the informatics education. The introduction starts with pointing that "the power of GIS for the humanities lies in its ability to integrate information from a a common location, regardless of format, and to visualize the results in combinations of transparent layers on a map of the geography share by data" and sadly adding that the existing GIS software was created for environmental planning questions and now it "requires humanists fit their questions, data, and methods to the rigid parameters of the software"  which makes it challenging in the extreme fussing GIS with humanities. 

I have personally experienced that while working on cultural areas visualization. And nothing else was as hard as to find a way to visualize just because the concepts themselves were not suitable for my task!

examining boundaries with example of archeological culture

Do exist cultural boundaries? Do cultures bound itself or just scientists draw it?

Social scientists are so much focused on the concept of boundaries, that there is no question it exists. It's long time it's proved people always have some concept of 'us' and of 'them' in their mind, it means socially they make distinctions. And so social scientists are interested in social phenomenas emerging due to such differentiation. There is a whole study of boundaries done. But the boundary concept is not full - it's just social boundary concept, concept mostly defined by self identification which might define or identify ethnos, but not whole ethnical culture and NEITHER archaeological culture. Archeologists define archeological cultures, which may be ethincal cultures, cultures identifying themselves as one, but it is never a rule. All if far from geographical boundaries as well as the culture and it's spread is understood differentially. Geographers try to unite all possible aspects, drawing and presenting the boundaries of cultural regions.

Let's look at some archaeological boundary of Lithuanian archaeological culture drawn.