On Thu, 13 Mar 2008, hadley wickham wrote: >> > In the trellis panel functions, or in the direct plot/image/lines etc >> > functions, you plot in data coordinates. The main thing that the plot >> > and spplot methods in package sp control is the aspect ratio. How else >> > do data coordinates differ from geographical coordinates when it comes >> > to plotting? >> >> Exactly. In fact I think that a grid panel might make it possible to >> insert an image backdrop behind spplot(), which was the original question >> from Dylan - it would make a nice student project in visualisation. >> Something like an sp.image() for sp.layout=, but using its own palette and >> being painted over by the "real" data. > > Another approach would be to develop a better interface between > spatial data and ggplot2, which provides much better support for layer > compositing (and in general for modifying a plot after you have > created it). There are some simple examples at > http://had.co.nz/ggplot2/geom_polygon.html and > http://had.co.nz/ggplot2/coord_map.html, but I don't know enough about > the problems of spatial data to be able to do it all myself.
Maybe, but as Wilkinson says, his proposal is not a GIS either. I'm sorry nobody replied to your question earlier about using mapproj. Even the way Wilkinson addresses things isn't going to deliver unless the data and the graphics stay very close together. This is the mapproj problem, the projected coordinates are an eclectic rendering, not something that can be used for anything else than display. Over thousands of km, the problems are not so clear, but over a couple of km they are showstoppers. It looks as though Simon Urbanek has been trying to "do it his way" for iplots by publishing a limited interface to PROJ.4 on CRAN as a proj4 package, presumably because there are real issues in providing proper support on OSX, and on Windows (I don't imagine that he didn't know that PROJ.4 is interfaced in rgdal, because I have asked for his help in finding a mechanism for producing rgdal binaries for OSX with minimal intervention). The Windows issues are fully addressed by rgdal (but not in proj4, there is no PROJ.4 share/), which he could have used, but chose not to. Perhaps I should ask again whether he could help automate the production of rgdal binaries for OSX? Yes, you are right that this needs doing in concert between people who understand both sides, the graphics side, and crucially the spatial data side, because the layering fails unless the data are correctly aligned. This constrains the ways the data can be represented, and the S data model of a two-column matrix with NAs to separate geometric entities is simply not sufficiently robust. Roger > > Hadley > > > -- 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: [EMAIL PROTECTED] _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo