I did something similat a few years ago with an artificial marine chart I use with models for teaching buoyage.
I selected an A4 ratio piece of the image and noted the edge numbers on a scrap of paper, then cropped the image and printed what was visible. I then backstepped until I had the whole image back again, selected another piece that "just" overlapped the first by a couple of mm and repeated the process.
Actually printing the image turned out to be the easy part. It was a nightmare trying to get about 24 A4 sheets lined up correctly so I could glue it all up. I'd never realised how much wet ink will alter the paper shape. How advertising posters manage I have no idea.
Richard