Dealing with a large map is often troublesome. They get torn and wrinkeled and caught by the wind, or you just don't have the space to unfold them.
About 15 years ago I came across a map that was folded and cut in such a way that even though it was about 1.5m x 1.5m, it unfolded to no more than magazine size.
I am trying to reverse engineer the design here.

If the first page was left a little wider than the rest, this might also be handy to look up values in a very large table and still be able to see the row and column headers, much like the Excel split frame function.

Step 1: Materials and Theory

You will need
- a map, or piece of paper for practice
- ruler or tape measure
- scissors

You will need to divide the north-south direction of your map into equal parts. The number of parts depends on the number of foldable rows you want. The more rows, the smaller the final product. The formula is 3 + (5 x #rows). This example will use three rows.

Mark the spots where you will fold the face of the map inwards, i.e. the 1st, 5th, 6th, 10th, 11th, 15th, etc.
You do not need to mark the remaining divisions.

Step 2: Make Only the Inward Folds

At all the spots you marked, make folds parallel to the edges of the sheet so that the map faces inwards. Do not make the outward fold yet.

Now, turn over the map and fold each of the longer divisions in half so that the previous folds match up. While you have some flex with the divisions in the first place, this needs to be fairly exact, or the map will tear or not fold flat.

Step 3: Make the Vertical Folds

The number of vertical folds is flexible. The very left and the very right panel should face up.

My sample map will have only four pages, so I folded it in half face-out, and then folded each half face in to match up with the center.

(Ignore the cut on the centerline for now, that comes in the next step...)

Step 4: Make the Cut(s)

Lie the map down with the flat sections resting right next to each other. I even taped them together on the back of my map for a neater result.

For each vertical face-up fold, cut down the fold to the flat section. Don't cut the flat section.

Step 5: Refold the Map

Re-fold the map like it was before the cutting step.

You should have something now that looks a little like a beat-up book.

Flip open the first/second page. Imagine you are getting into town from the south-west. As you drive north, flip down each successive flap. As you reach about the middle of the map you turn east to head downtown. Count the number of flaps you folded over. You can leave the flaps as they are, or fold them back. Flip over to the third/fourth page, and flip down as many flaps as on the previous page to bring up the part of the map you are now driving into.

When you are done, go to each page and make sure all the flaps are up.

The original map I saw was glued into a heavy-duty rubber cover. I had it in the glove compartment of my motorscooter for years, and you would not have known it for the wear it (didn't) show.