Outside of Western Europe and the USA, finding accurate large scale topographical mapping for wilderness backpacking/trekking trips can be a problem. Often it is either difficult to source or ruinously expensive – or both.
There is a surprising source of topographic mapping – Soviet military maps. During the cold war, the Russian military undertook a staggeringly ambitious plan to map the entire world. Following the collapse of the USSR, some of those maps leaked out to the West and are now publicly available. They are a great resource for backpackers/trekkers, being highly detailed and generally accurate.