I tried to use the GeoNames RDF file, but it does not seem to be valid RDF.
This can be tested with the following command:
$ curl 'http://download.geonames.org/all-geonames-rdf.zip' | gunzip | head
This shows that the GeoNames RDF file contains snippets of RDF/XML interspersed with loose URLs (see below). Since this is a non-standard format, I assume that there is a common procedure or script to transform this file into a valid RDF file.
It's a somewhat strange format. It's a url followed by rdf/xml for that url. I put together a short bash script to output it to a single n-triples file. That I'll post when I find it. It takes a while, maybe a day, and results in about a 600mb file compressed.
I've asked for the mappings used to generate the rdf several times but for some inexplicable reason they won't share it.
I guess we will have to add a feature to our LOD Cloud download script that allows custom code to be applied to the downloaded source data file, prior to uploading it to our triple store. This will allow non-RDF to still be uploaded as RDF.
I'm not sure what the benefit is of publishing data in formats that are not standardized, but at the same time GeoNames is still a great resource, so I guess we must invest this extra development effort in order to be able to include it.