Surveyed Maps are collected by Surveyors, but thematic Maps are interpreted by specialist professionals.
Surveyed Maps are highly accurate, and so are legitimately scaleless in a GIS. However, Thematic Maps contrast to Surveyed Maps because the scale of a Thematic Map is far more about the scale of its collection than the scale of its display.
It’s not that you shouldn’t bring thematic maps into your GIS, it’s just that you need to understand the limitations of the maps that you’re using. That’s what this video is about.