Hi John,
As far as I know,there's a work having done in Spatial and Temproral RDF[1][2]. This work supports indexing spatial data types like lines, polygones,.. by and operators on spatial objects.
Danh Le

[1] Supporting Complex Thematic, Spatial and Temporal Queries over Semantic Web Datahtttp://www.springerlink.com/index/4872811403q60723.pdf

[2] Sheth, Amit; Perry, Matthew, "Traveling the Semantic Web through Space, Time, and Theme," Internet Computing, IEEE , vol.12, no.2, pp.81-86, March-April 2008

On 14 Apr 2008, at 11:43, John Goodwin wrote:
>
> Hi Steve,
>
> Thanks for your reply. It would be nice to generalise this to other
> spatial datatypes like lines and polygons - but certainly would be
> non-trivial I'm sure.
>
> Has much work been done on spatial indexing of RDF?