A hard copy map is essential for Salcantay. A guidebook is not enough.
We were frequently confirming the best route with locals & with guides from other groups. Conversational Spanish is a big advantage.
Luckily, the farmers & herders were friendly & welcoming.
The best map is IGN 1:100,000 machupicchu map (sheet 2344, 27-q) but it does not have the trail marked on it. You need the Lonely Planet Trekking in the Central Andes guidebook as well.
Buy that map (when you get to Cuzco) from the South American Explorers Club. Occasionally they run out. You can also find it in some of the shops in the town centre.
If you want a map in advance of arriving in Cuzco, the Machu Picchu Map by ITMB by Andrew Duggan, International Travel Maps, should be just as good, though we have not used it.
You may want to consult online maps (they open in another window) while planning your hike:
