How to create segment a large model of landscape into smaller sections that can be higher resolution? I hope to make a 3D model of existing landscapes in blender, with the hope of eventually adding them to video games that allow you to create your own maps. I tried using the following two tutorials with no luck: https://youtu.be/BXDSfrzR0zI and https://www.beamng.com/threads/tutorial-level-building-with-lidar.39370/

With the video, I do have 3D maps, but I think I have too large an area with too low of a resolution. This is because when I try to zoom in, it seems the roads are a bit blurry. I am trying to start out with somewhat large areas, like the island of Nusa Tenggara Timur in Indonesia, with the hopes of slicing out a smaller section that can be used in a game without crashing. I am quite new to blender and while I can follow along the video tutorial, I’m not 100% understanding everything I’m doing and what the alternatives are.
To answer your question. Slice down your original hight map into smaller parts. So you can assemble multiple so called map tiles into one high resolution map.

For large detailed enviroment usualy tiling maps are used in game engines. The heightmaps are loaded directly in a shader - in modern games with adaptive generation of geometry depending on the distance you can actualy see (Tesselation). 
If you generate a high resolution mesh for each map tile you most likeley will run into memory issues.