What I'm missing in your mail is an explanation of what you want to use
your encoding for. Is it important for you to capture the distinction
between a geopolitical name and a feature of natural geography? If
you're just going to create multiple output formats (html, pdf, etc.)
the semantics of the different name types are not that important. Do you
want to e.g. create indexes that distinguish between the two?
Your idea of using
> <placeName><geogName type="planet">Vinyemeer</ and so on.
suggests you want to somehow capture that a planet may be both a
geopolitical unit and a feature of natural geography. But in fact by
using both tags you're also obscuring the difference. Why not use just
<geogName> and, if you want to positively identify the political
organisation of the Martians, rather than the planet where they live,