Tiny Terrain is a lossy Terrain Data compression technology for Unity Terrain Engine, which allows you to reduce the size of the data that Terrain takes in the project many times and significantly reduce the size of your application.

Terrain Quality Manager
Terrain Asset For Unity
Best Reviews
Indispensable
sjm-tech
Great tool! ... Did save me a ton of hours ... a few clicks and the job is done... thanks!
Perfect
magique
I've been wanting this one for a long time and I finally picked it up and it was worth every penny and then some. I converted my 2049 resolution terrain to 513 in just a few clicks and everything looks and works perfectly. The big question is, why on earth after all these years can't Unity just provide this right inside Unity? This is a must have.

Terrain Quality Manager is a tool for changing the resolution of Unity Terrain maps (Heightmap, Detailmap, Alphamap and Basemap) without losing data.
If you want to increase the quality of terrain, or optimize terrain for better performance, with this tool we can do it easily and quickly, with just a couple of clicks.
Features: