I’m mapping in Switzerland.
One of the most important orientation characteristic in the alps are rocks/cliff and scree.
But there is no rendering for it. And the other side there is a rendering for landuse meadow and farmland.
This is just overloading the maps and is only temporary. Or I’m tootally wrong???
Thanks for your help.
The rendering can be a bit anglocentric. Even though we do have some scree and rock faces, especially in Northern Britain, the vast majority of the country, and many other countries, doesn’t have much of it and so it isn’t rendered.
natural=cliff does render. natural=rock doesn’t.
But don’t worry about the renderer, get the data into the system and maybe set-up a custom render. As long as the data is in, it will eventually get rendered somewhere. 
If it really concerns you, you can report it on Trac under Mapnik, perhaps file it as type enhancement and milestone wishlist to make clear that it isn’t a report of a defect but a request for a new rendering rule.
Welcome to the forum, by the way.