Yam Fries with Yogurt Dill Sauce

What is the difference between a sweet potato and a yam? I always thought they were the same. Some other people, including my dad, always said that it was a regional dialect, in the north sweet potatoes and in the south they called them yams. I bought this, thinking they call all "pop" cola in the south, so why wouldn't the exchange convert to vegetables.
However, I am wrong, my dad is wrong, and all the others who thought/think they are the same thing. There's all sorts of information on the good ole' reliable world wide web about the difference of these two vegetables. Region does play a part, the yam coming from latin America, the sweet potato is found more north. The yam has more natural sugars in it and can grow up to 7 feet in length!! At About.com: Home Cooking there is some great information along with links that compares the difference between the two.
Well, sweet potato fries and yam fries .... apparently there's a difference.
I picked up some yams. And they really make some delicious fries. A yogurt dill dipping sauce is the perfect accent. This 'pie will yield a giant plate of fries (more than enough for four people) and same goes for the sauce.

Yam Fries 
-2 medium sized yams - sliced into thin strips
-1 tbsp olive oil
-dash of salt
-dash of cayenne

Preheat the oven to 450. Layout the cut, sliced yams on a cookie sheet and drizzle oil over them, toss them so it gets on both sides. Sprinkle salt and cayenne over yam fries. Place in oven and bake for about 10 minutes, flip them over and bake for another 10 -15 minutes until they turn golden. If you like crispier fries, lay-off on the olive oil and bake a bit longer.

Yogurt Dill Sauce
-1 cup soy yogurt - I use the silk brand
-juice from 1 lemon
-2 teaspoon dried dill
-dash of salt

Mix all together in a bowl. Serve on the side with fries. ENJOY!