The fastest and safest way to go for this is to go down the colony path and pick up the exploration idea and send out explorers and conquistadors to every corner of the world. But it doesn't matter how the world is revealed, you can just sit and wait for most of the world to be revealed for you but there will most likely be a deep part of Africa that you won't just get by itself unless you spread your country towards those corners of the world. Note that lakes count as wasteland provinces, so don't worry if there is white fog over some lakes when going for this.