How to create animated heatmaps?

Hi @sean_lilley , how I can replicate this example to make it work with terrain elevation data so that I can shade different parts of the terrain (within the rectangle, not the whole globe) based on elevation information?

I cannot visualize how height will map with the texture. How I can make elevation information available in shader? In this example, we use st to pick the colour, but how about elevation?

Also, it’ll be helpful if you can explain what is this texture coordinate (st) and how it’s different than fragment coordinate. How texture coordinate and texture work together ?