Creating a field of contours/land morphology with gradations of density and size

Hi there,

I'm interested in creating a landscape surface/field (or alternatively a 2D pattern that can then be patched into a surface) using a series of constraints. The effect I'm after is essentially a series of rolling hills/landforms, whereby the landforms are higher and denser in the middle, and then reduce in both height and density towards the edge of the field.

I require the contours to be of varying shapes (I have attached an image below for reference). I have tried to do this by elevating multiple points on a grid using a patch, but cannot achieve the desired result. I have also attached an image regarding the gradations of the field pattern that I'm after.

Does anybody have any pointers as to how I would commence such a task? I've been told that vector and attraction points could possibly do the trick. Any help would be incredible.

Thanks in advance,

Dan