How can I create landspace 500 meters?

Hi I want to create landscape 500 meteres, Can you explain me How I must set this :

I would start here and work backwards from this:
https://forums.unrealengine.com/development-discussion/content-creation/28153-calculating-exact-map-size

To understand the concept of vertices and overall size this is a very useful resource:

Remember 1 unit in Unreal Engine is equal to 1cm.

Hope this helps, good luck