

Hi all,
 
I sent a message to Roger Bivand a couple of days ago, and he suggested rather posting it here, so other people can read the answers later on as well.
All comments are quite paraphrased for better general understanding, so none are our direct quotes anymore!
Especially the later questions are yet open for discussion!
 
 
> would it be a good idea for the helpfile to gUnion to include a 
reference to unionSpatialPolygons (in the package maptools) for an 
ArcGIS-like operation of "dissolve"?
 no, because maptools suggests rgeos, but not the reverse
gUnaryUnion is the function to dissolve Polygon Shapefiles.
> To use it on one of the AttirbuteTable columns, I successfully used gUnaryUnion(MyShapefile, MyShapefile$ColumnName)
 
 
> I need a SpatialPolygonsDataFrame for export, i.e. to use for writeSpatialShape
gUnion etc. return SpatialPolygons objects. The documentation of the sp classes should help.
> writeSpatialShape by the way does not return any error or warning when used on gUnion results! (seems to do nothing at all, at least it's not writing files...)
 
 
> selecting by attribute table and then writing a new shapefile to disc: 
> writeSpatialShape( Shapefile[ Shapefile$Column=="someStateName",] , "NewShapefileName.shp" )
> If I don't look at any projection issues (I know I'm lazy, but I guess I'm not alone there), I of course loose the .prj file.
> Would it be a good default to just copy the one from the read-in shapefile, maybe with a warning?
 
 
> It's kind of hard to start handling shapefiles with R all by oneself, I couldn't really find any introductory works on it online. 
> Did I miss books or good tutorials out there?
> Would it be a good idea to create one? Who would be interested in reading and especially in writing that? 
 
 
Greetings from Potsdam, Germany!
Berry
 
PS: Sorry, if anything sounds downright stupid - I started serious shapefiling only a few weeks ago.

 		 	   		  
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