The base of this Pottery Barn map uses Polyester Brushed Tricot, which is compatible as the loop side for the hook Velcro. That is why the "felt" accessory pieces use velcro on the back. Real felt boards do not use Velcro, the felt just sticks to the flannel board by itself, with friction.(or maybe with static electricity?)
If you use felt for the continents, or base of the map, velcro will not work on the felt, alone. You will need to use the loop velcro pieces on the base, wherever you want the accessory pieces with the hook velcro to stick. Hope that makes sense!
I do not know of a stateside source for the Velcro compatible Poly. Brushed Tricot. This is a fabric that is manufactured in Taiwan or Korea and shipped to China and used to make just about every toy and soft goods product imaginable. I don't know of another fabric that is Velcro hook fastener compatible.