BLANDENIER Lucien wrote: > Dear all,
Hi Lucien, > I'm trying to merge all polygones with the same attribut of a shapefile. I > saw it is possible to merge adjacent polygone with r.dissolve Small correction: it is v.dissolve (all v.* modules operate on vector maps as opposed to r.* modules which operate on raster maps). > but I didn't found how to do this with polygones that are not adjacent. Is > there a way to do this? I don't know/I don't think so. GRASS' vector model is a topologically aware system. This means that it "understands", exactly, adjacent geographic components. Being so, by design, supports a clean geometry (for example, non duplication of features) and sound vector-based analyses. If I get the "picture" correct, there is no possibility to topologically merge distinct and spatially non-related geographic features. > My goal is to minimise the number of feature into my table in order to have > only one feature by category, but containing several polygones. What is the reason to worry about the number of vector features in a vector map? The only way to minimise features is by eliminating them, which is rather unwanted. You might want to read - "Vector object categories and attribute management" section in the "Vector data processing in GRASS GIS" manual: <http://grass.osgeo.org/grass64/manuals/vectorintro.html> - "Developer's Vector FAQ" <http://grass.osgeo.org/programming7/vlibFAQ.html> Each unique vector feature holds internally (that is, not exposed to the user) a unique "feature id" (this is a 1:1 relationship). The user can, however, use the concept of Categories (another identification number), to assign a vector feature to a category. Categories are not unique and they _can_ be (mis-)used to link to several vector features (this is a "1 Cat":"Many vector features" relationship). Note, the user can use them as being unique! Also, any vector feature can be linked to several category ids (this is a "1 Vector" : "Many Categories" relationship). The other interesting concept, in GRASS GIS, is the one of multiple layers. The user can link multiple attribute tables by using multiple layers (<http://grass.osgeo.org/programming7/vectorlib.html#vlibCategoriesLayers>). So, maybe (inside GRASS GIS) you simply need to assign the same category to many polygons? Best, Nikos _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
