You have a very interesting project. What happens if you put your maps and elevation data on a 'sphere', to model the world as 3D? You can then leverage a GPU t

You have a very interesting project. What happens if you put your maps and elevation data on a 'sphere', to model the world as 3D? You can then leverage a GPU to render a view from one vertex to then determine what is furthest away yet visible from that vertex. The vertices can then be given some type of heatmap colour and an interactive tool made. A full GIS tool isn't needed for this, with Blender and three.js there are all of the tools needed.