So I'm totally new at Blender. I have a drone-scanned image of a city that I need to simplify. I need the poly count really low but still keep the high-res imagery. What I would like and need is to turn the mesh into a single poly like I highlighted in the image. I'm pretty sure I know the answer to this but is there a simple way to do that?
One way to simplify geometry would be to use the Decimate Modifier.
Add the Decimate modifier set to Collapse, and turn down the ratio.
Click Apply, if you want to edit your geometry manually after.
If you want to see the polygons like in my gif, enable Wireframe in the Overlay menu.
Then just manually select and join faces into one.
Vertex > New Edges/Faces from Vertices
There are also other ways to simplify geometry, I didn't want to overwhelm you.
This tool can simplify your mesh by dissolving vertices and edges separating flat regions.
Reduces detail on planar faces and linear edges with an adjustable angle threshold.
Always dissolve vertices that have two edge users at boundaries.
Prevent faces from joining when they don’t share certain properties (material for e.g.).
(Blatantly copied from the blender manual https://docs.blender.org/manual/en/latest/modeling/meshes/editing/basics/deleting.html)