I want to introduce you a cool thing. You know that making a large terrain full of mountains and valleys is some how tedious. But don’t worry. You can get the height map from http://terrain.party.(if you don’t know what is heightmap check “jMonkeyEngine 3 Tutorial (10) - Hello Terrain” in JME help menu )
just search for city name then click on export button. then you will get image texture of heightmap .
I hope you enjoy this.