Open-Source Clojure Library for Geospatial Information
blog.factual.com
blog.factual.com
The only caveat looking at this is that the geometry computation is not suitable for some types of geospatial analytics. This has been a persistent gap in open source geospatial tools. The challenge is that closing this gap is a pretty esoteric topic in applied mathematics that only a handful of people are really qualified to address and few of them seem to be contributing to open source. Still, any progress is good.
http://alienspacesciencenews.files.wordpress.com/2013/10/an-...
The Local Datum could be NAD83 or what-have-you based on where you are on the surface. Using the local datum gives better distance measurements and more accurately can represent elevation.