@RickB - I’m trying to do something similar - dynamically creating polygons and adding them to a raster overlay of a tile set. The difference is that I want each added polygon to be a different color. I’m trying to achieve that using a dynamic material instance - and this is the point at which I’m failing.
I’m trying to do it all in Blueprints (and it’s not working).
I’ve posted here: How to add colored polygons at runtime?
I may need to switch to C++. Is there any chance you could share your code as it will give me a great head start? (Of course, I fully understand if you can’t - but, hey, it doesn’t hurt to ask 
)
Also do you know how to set the layer name of a Material Instance and/or to set parameters on a Material Layer Blend - at runtime.
Thanks.