Generating polygons.

I would like an opinion on this as I’m trying it but don’t know how practicall it is and how much overheads it’s gonna have. I load a map from a file, but this file only contains one vertex, the alignment, etc.
I then push the array with the vertices through a function that generates the other vertex coordinates. It does work, but I have not yet loaded big maps, and applied textures lights etc. It’s just two coloured traingles making up a quad at this stage.
This makes for less complicated and smaller map files. Will it kill the system if it has to generate all those vertexes? (if the map is big)