On this page I describe how to use the free Foxit pdf reader to easily navigate the Cahill-Keyes Multi-Scale Megamap Beta-2 pdf at its humongous size of over 9,000 square feet: 40 m x 21 m, or 132' x 69' (a free 35 MB download).
Even I, the map's designer, tended to get lost in transit when trying to roam the Megamap at its full original scale of 1/1 million. But unlike Adobe, the Foxit pdf reader solves that problem, and makes it a breeze to instantly relocate to any sector, zooming in and out, and panning smoothly in any chosen direction. Using Crimea as a test case, we zoom in at increasing scales of 1/10 million, 1/5 million, 1/2 million, and 1/1 million. (Another map and two more remarks below.)
That one above is only an outline map, but it has very high resolution coastlines and borders.
Meanwhile, Duncan Webb has just published a 61" Cahill-Keyes wall map poster at 1/27 million, with colors, countries, capitals, and more.