Both circles and sets are considered abstract objects. I can visualise a circle in my mind (can 'see it through my mind's eye') but can't visualise a set or a number. I have no picture of a set in my mind. This makes me wonder if there are two types of abstract objects, those that can be visualised and those that can't be.
Are there two types of abstract objects, those that can't be visualised and those that can be?
If yes, are there terms to mark that distinction?