Not all VTTs are browsers and not all of them load all of the map as images either. And, even if all of it is based on images, then some of them reuse the same image for icon stamps so that you don't need the whole image with all occurrences of the stamped icon - just the one stamp and the locations of where they all are. So not all of them have a fixed pixels per tile value and some don't even use square tiles anyway.

So... which VTT is this big map intended for ?