Check this map i generated:
I seeded a sine wave to act as a mountain range. The lower portion of the sine wave looks fine, but the upper side is thin, the algorithm did not do its magic there (expanding with some noise the seeded values to generate wider mountain ranges and then some hills (brown and light brown)).
Also, the whole continent shape is not affected by the sine wave. Ideally, it should be like a "S" as the mountain range pretends to be.
I bet this is how the diamond square algorithm takes the values it uses to make the average.
If not seed the center point of the map, i can not generate a continent, it just makes a pelinesque noise of random hills.
Basically, i'm having some hard time trying to control the noise with seeds and toying with amplitude and randomness reduction values.
I need some experienced people in world generation and noise to help me out!
(PS: red dots are rivers).