Super cool, thanks for sharing!
Thanks for comment Nathaniel,
from technical point of view ShareMap is executing query on Natural Earth data imported to PostGIS database. Currently queries are limited to bounds and importance but in future we will try to extend them
If anyone will need in future database dump of this PostGIS DB I will be happy to provide it (for me conversion SHP file to DB took some time)
@jkan997: The new 2.0.0 rc2 version of Natural Earth should be much easier to import into PostGIS. Let me know your experience: http://kelsocartography.com/blog/?p=4246
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