I wonder if this is related to using space-filling curves for indexing:  <a href="http:&#x2F;&#x2F;www.drdobbs.com&#x2F;database&#x2F;space-filling-curves-in-geospatial-appli&#x2F;184410998" rel="nofollow">http:&#x2F;&#x2F;www.drdobbs.com&#x2F;database&#x2F;space-filling-curves-in-geos...</a><p>One of the professors at my institution is big in that field.