TLDR: It's easy to explain confusing a rope to be a snake. But how is spatial dimension imagined? Does Brahman have spatial dimension. If yes how is that not Bheda? If no, then how is spatial dimension created by maya?
The classic Advaitha metaphor is the pot and house, Ghatakasha and Matakasha. Where the Space inside House is divided by the wall of Pot into Space inside pot.
Here wall of Pot is the Upadhi, which out of One Space(House Space) demarcates and creates two Spaces(House Space and Pot Space). So if there are many Pots people will think there are many Spaces. But there is only one House Space which is divided by the wall of Pot into multiple Spaces.
Advaitins say in the same way Upadhi made of Maya, creates multiple entities by demarcating Brahman, and creates the illusion of duality. These multiple entities are an illusion as the Upadhi itself is an illusion as it is made from Maya, so in reality, there is only one entity, Brahman.
So far so good, but Shri Madhvacharya in his Upadhi Khandana, asks a very interesting and important question.
He says in the analogy offered the Space is equated with Brahman. But Space has spatial difference (Deshiya Bheda). You can travel in Space, you can go from ONE place to ANOTHER place in Space. The wall of Pot only divides this already present Bheda. But in Brahman there is no Bheda, let alone Deshiya Bheda. So what exactly does Maya Upadhi divide?
How does Maya Upadhi create Bheda in Abheda Brahman? This is not explained in the exmaple.
Are there any answers to this objection from the Advaitic tradition? What is it?
The above objection is my paraphrasing of Shri Madhvacharya's objection. In his original work he also discusses a vikalpa and asks questions regarding Upadhi creating Bheda which lead to Anavastha in logic(Argument ad Infinity). I could not quite understand this.
It would be helpful if the answer includes a brief explanation and clarification of the objections raised by him. I here cite a relevant extract of Upadhi Khandana.
The position that Upadhi gives rise to difference is also untenable. Upadhi can only highlight an existing difference and not create it afresh. Like in the case of a pot that could only be a medium to demarcate a region of space that already exists.
If the pot were to create a region in the space afresh, would it do it by contacting a region of space or otherwise? In the former case, one must agree that the region already exists apriori. If the pot could demarcate without contacting the region, then anything can demarcate anything. Also, is the contact of the pot accepted to be only to a region or to the entire space? It cannot act as a demarker if it contacts the entire space. If it is contact a region, that means the space has several such regions by default. If not, there will be an infinite-regress.