connecting subgraphs
On Wed, 27 Oct 2010, Yan Boulanger wrote:
Dear Rsig community, I'm quite new to R-sig. Here's my problem : I have a set of polygons representing Canada's ecodistricts. Although the great majority of polygons are contiguous, few are "isolated" from the main "polygon mass". I created a nb object using the poly2nb function. When I use the snap function (let say 60 km), it links all polygons together, without leaving unconnected subgraphs. Obviously, this also create additionnal links between polygons that are not "really" contiguous INSIDE a given subgraph. I would like to keep only the additionnal links that connect the subgraphs together using a threshold distance (60 km). My question is : is it possible to connect subgraphs that are isolated from each other by a certain threshold distance without doing it manually ?
Not with polygon representation at present, although the rgeos package on may make it possible to buffer around member polygons in each subgraph to identify the closest ones. With centroid representation of the polygons, one could first find the members of subgraphs, then check distances. But this wouldn't be the same as polygon representation. Roger
Thanks in advance, Yan Yan Boulanger Dendrolab - Datation de b?timents patrimoniaux par dendrochronologie www.dendrolab.ca info at dendrolab.ca Universit? du Qu?bec ? Rimouski D?partement de Biologie Centre d'?tudes nordiques 300, all?e des Ursulines Rimouski, PQ G5L 3A1 (418) 723-1986 poste 1482 [[alternative HTML version deleted]]
Roger Bivand Economic Geography Section, Department of Economics, Norwegian School of Economics and Business Administration, Helleveien 30, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43 e-mail: Roger.Bivand at nhh.no