Creating flat areas that blend well?

Hello,
I’m currently trying to generate a world (not a terrain area) with use of masks to delimit certain generation types per area.
One area that is giving me trouble is cities, i want to leave flat areas for later placement but making something completely flat is looking really bad as it doesn’t blend with the sides.
Any tips on how i could do a 2 step process to have an area A blending from noise on the outside to nearly no noise inside and then an area B inside of it that is completely flat so you wouldn’t feel there is a huge gap whenever you ender a city?
Thanks!

Hi Ronan,

Have you looked at using a Layout Generator device? If you input the terrain into the primary input of the device, you can place shape regions at any elevation you want with a controllable falloff – this lets you slowly damp out the surrounding terrain until it hits the level region (and of course, if you reduce the strength of the shape, you can retain a bit of character within the flat region)