You should check two excellent books by Hanan Samet "The Design and Analysis of Spatial Data Structures" Haman Samet Addison Wesley 1990, ISBN: 0-201-50255-0 "Applications of Spatial data Structures" 1990, ISBN: 0-201-50300-X This is the most comprehensive source that I am aware of. Mike Gigante, mg@godzilla.cgl.rmit.oz.au