In Heart of Africa you must have more than or an equal number of terrain cards to play over another person. If one person has 3 terrain cards face up and I have only two cards face up but I hold a wild card, can I play the route doubling my points. Or can I only play based on the number of displayed terrain cards? To me the logic is you can only play if you have and equal number or more terrain cards as the opposing player and Locomotive (wild) cards cannot be counted toward your displayed terrain card face up count.
Yes you can use locomotives to reach the number of Terrain cards shown by an opponent. Indeed this exact situation is shown in the rules.
Using Locomotives as Wild Terrain cards
During his turn only, a player may opt to use some of his Locomotives as Wild Terrain cards instead of Wild Train cards. Each Locomotive played this way is worth 1 Terrain card of the player’s choice. All locomotives played as Wild Terrain cards must be discarded. They go on the Train discard pile.