How do I set a tile at a certain point?

I currently have a way of randomly generating maps by spawning sprites but this is bad for performance.

I was wondering how I could create a specific tile at every point where there is a floor sprite.

Here. Capx is commented; should be self-explanatory:

https://www.dropbox.com/s/yysabadof5yt3 ... .capx?dl=0

Here. Capx is commented; should be self-explanatory:

https://www.dropbox.com/s/yysabadof5yt3 ... .capx?dl=0

Thanks!