[R-sig-Geo] Map labels

[tom sgouros]

Is this another way to say that I've stumbled onto one of the borders
between the set of tasks that R does well and the set of tasks I should
use a GIS for?  Or should I persevere with R on this?

Second question: if I want to just do this assembly myself, so to keep
some control over placement, is there an add-a-Polygon-to-my-Polygons
method, or do you have an example of something like that?

Thanks for the help,

 -tom


Roger Bivand <Roger.Bivand at nhh.no> wrote:

> > This doesn't, though.  When I read in my data, the IDvar is supposed to
> > be the column that is unique for each record, correct?  But there are
> > several records (closed polygons) for each town.  These are linked by
> > another variable.  The coordinates(rep.map) gives me a list of 419
> > coordinates for all the closed shapes, not 75 coordinates for all the
> > towns.  How do I get the biggest polygons for each town?  I have an Area
> > attribute, so I guess I can just calculate it.  Is that the right way to
> > go, or is there some method already existing for this?
> >
> > I thought maybe my readSpatial... was done wrong, so I changed the IDvar
> > to point to the iD for each town, but that gives me an error saying that
> > duplicate row names are not allowed.  Is there a step I needed to take
> > to link the polygons?
> 
> Yes, see the unionSpatialPolygons() function in maptools. It uses
> functions in gpclib to dissolve boundaries between member entities if
> they touch, so makes a Polygons object with possibly multiple member
> Polygon objects from multiple Polygons objects with the same ID values
> (towns for you). You then need to drop rows from the data.frame
> (as(rep.map, "data.frame")), and re-assemble using
> SpatialPolygonsDataFrame() with the row.names of the data.frame set to
> the town IDs used in unionSpatialPolygons().
> 
> The mess is caused by the underlying data being kept in OGC SFS
> (simple features) form, which does not store well in shapefiles (a
> similar remark could be made about SpatialPolygons objects, which are
> more like shapefiles than like SFS).
> 
> The gpclib package should not be used if its license conditions are
> inappropriate. A free software alternative is being prepared.
> 
> Roger
> 
> >
> > Thank you,
> >
> > -tom
> >
> >
> 
> -- 
> 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
> 


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