I have no idea what your talking about there.
-A quadpatch is a square bunch of quads (a square made of 2 triangles)... a simple flat "grid" mesh if you will.
-Dynamic means they only get created from a memory template when you need them and removed when you dont. So you can create draw-in draw-out zones off screen.
-A Large texture drawn in say paintshop, complete with roads, mud, grass, paths etc is then put on each quadpatch.
The textures are designed beforhand so their edges work with both each other, basically in the same way as normal 2D terrain tiles would, just on a much larger scale allowing you complete drawing freedom except for at the very edges (because of the need to tile).
These textures can then be used as a template for creating heightmaps (or you can use one of the many Wysiwyg editors out there).
Normally 1 large texture would look blurry in say.. an FPS game, but because its top down, if you make one terrain block(quadpatch) the correct size, -so that when viewed with the camera from above, it is drawing close to your screen or viewport's size then the texture would appear similar in resolution (with mipmapping tuned off) to when it was drawn.