If you want a base map to add your polygons to, you can use the Maps package in R, or plot a map from a shapefile or arcinfo coverage using Rmap or maptools libraries (for shapefile format) or RArcInfo (for e00 or avc formats) in R. To add your polygons to the figure just use polygon(). If you need to reproject the coordinates in your polygons you can use mapproject() in the mapproj library or project() in Rmap(). I prefer project() (it can convert from a projection to geographic coordinates (ie, lat/lon), while I think mapproject() just takes geographic coordinates) but mapproject() has more documentation. Both use proj4 library (libproj), so you will need to install that. To use shapefiles you need libshp. I think Rmap is still not distributed via CRAN. You can find it at http://www.maths.lancs.ac.uk/Software/Rmap/ I've linked the documentation for the proj4 library to Barry Rowlingson's Rmap documentation, which can be useful when you are re-projecting coordinates. If you want it, the zipped html files are ~9 MB. The original sources are on the web of course. areapl() in the splancs library can calculate the area of a polygon. Anthony L. Westerling Climate Research Division Scripps Institution of Oceanography University of California, San Diego 858 822 4057 leroy at ucsd.edu
Date: Wed, 30 Mar 2005 11:42:17 -0800 From: "Rick Reeves" <reeves at nceas.ucsb.edu> Subject: [R-sig-Geo] Reading and projecting lat/long point coordinates using R? To: <r-sig-geo at stat.math.ethz.ch> Message-ID: <000001c53560$9484c970$8bdc6f80 at BURAN> Content-Type: text/plain; charset="us-ascii" Hello: I've searched the literature, havent found an answer, so here goes? We have a set of polygon features defined as a series of unprojected vertices represented by lat/long pairs, in an ASCII-format file. We need to display (on a map-like plot) and then calculate the areas of the polygons, and would like to do this entirely within R if possible. Is there a map projection package for R? Or, has anyone solved this or a related problem using R? I could do this with the MATLAB mapping toolbox, but prefer to use R if possible.... Thanks, Rick Reeves Scientific Programmer / Quantitative Analyst National Center for Ecological Analysis and Synthesis University of California, Santa Barbara 805 892 2534 reeves at nceas.ucsb.edu ------------------------------
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