Hi Pierre, I think intersect.nb in the spdep package is what you are looking for? Have a look at the example there, looks quite similar to your problem. HTH, Jens
+++++++++++++++++++++++++++++++++++++++++
Dipl.Biol. Jens Oldeland
Biodiversity of Plants
Biocentre Klein Flottbek and Botanical Garden
University of Hamburg
Ohnhorststr. 18
22609 Hamburg,
Germany
Tel: 0049-(0)40-42816-407
Fax: 0049-(0)40-42816-543
Mail: Oldeland at botanik.uni-hamburg.de
Oldeland at gmx.de (for attachments > 2mb!!)
Skype: jens.oldeland
http://www.biologie.uni-hamburg.de/bzf/fbda005/fbda005.htm
http://jensoldeland.wordpress.com
+++++++++++++++++++++++++++++++++++++++++