The first picture in in Retiro Park. My suggestion is to either just get the monument (without the lake) or get the lake rectangular. I like more the first option... Place it in the middle of Retiro.
The second picture is Puerta del Sol, which is the "city center", therefore should go in Centro
On the names, There is no optimal solution as you have reshaped the "distritos" a bit, however they are somehow better with my proposal.. Or at least that's my opinion.
BTW, as you like pictures, here is one more:
Plaza de España: http://t3.gstatic.com/images?q=tbn:ANd9 ... TPqv9Q&t=1
) This one would go either south of centro or if it's too crowded in Arganzuela by the river.
There are other wonderful places, like "Plaza Mayor", "Neptuno", "Museo del Prado" but as I said all go to Centro, and I don't see enough space. If you want I can share some pictures and place them...