It's always a good idea to have a panel of regular pencils about different hardness : a hard 2H for a light sketch, medium HB for first details, soft 2B and 4B for shading and texturing are those I use the most. The advantage it that you can make the tip very sharp (well, less with 6B or 8B) with a knife or a regular sharpener. In my opinion, charcoals are less adapted for maps who requires a high detailing level, but are incredibly expressive for quick sketches like landscapes or portraits