---------- Forwarded message ----------
From: Markus Loecher <markus@sensenetworks.com>
To: Patrick Crutcher <pcrutcher@gmail.com>
Date: Mon, 18 Jan 2010 11:31:05 -0500
Subject: Re: Plotting shapefiles on top of Google map tiles


sorry, I was not at a computer that could run R last night when I came up
with the code, it needs some modification:

 shp=importShapefile(shpFile,projection="LL");
 bb <- qbbox(lat = shp[,"Y"], lon = shp[,"X"]);
 MyMap <- GetMap.bbox(bb$lonR, bb$latR, destfile = "DC.jpg");
 PlotPolysOnStaticMap(MyMap, shp, lwd=.5, col = rgb(0.25,0.25,0.25,0.025),
add = F);

and for an example that color codes the polygons individually

#North Carolina SIDS data set:
 shpFile <- system.file("shapes/sids.shp", package="maptools");
 bb <- qbbox(lat = shp[,"Y"], lon = shp[,"X"]);
 MyMap <- GetMap.bbox(bb$lonR, bb$latR, destfile = "SIDS.jpg");
 #compute regularized SID rate
 sid <- 100*attr(shp, "PolyData")$SID74/(attr(shp, "PolyData")$BIR74+500)
 b <- as.integer(cut(sid, quantile(sid, seq(0,1,length=8)) ));
 b[is.na(b)] <- 1;
 opal <- col2rgb(grey.colors(7), alpha=TRUE)/255; opal["alpha",] <- 0.2;
 shp[,"col"] <- rgb(0.1,0.1,0.1,0.2);
 for (i in 1:length(b)) shp[shp[,"PID"] == i,"col"] <-
rgb(opal[1,b[i]],opal[2,b[i]],opal[3,b[i]],opal[4,b[i]]);
 PlotPolysOnStaticMap(MyMap, shp, lwd=.5, col = shp[,"col"], add = F);

Markus

On Sun, Jan 17, 2010 at 9:13 PM, Markus Loecher <markus@sensenetworks.com
>wrote:

> Good question, I should have added a proper example to the
> PlotPolysOnStaticMap() function, which I wrote for that exact purpose.
>
> One way of overlaying, e.g. Census polygons on a Google static map would
be
> the following:
>
>   require(PBSmapping);
>   shp=importShapefile('bg11_d00.shp');
>   bb <- qbbox(shp[,"X"], shp[,"Y"]);
>   MyMap <- GetMap.bbox(bb$lonR, bb$latR, destfile = "DC.png");
>   PlotPolysOnStaticMap(MyMap, shp, lwd=.25, col = 'lightgray', add = T);
>
> Here, I use the package PBSmapping to read the shapefile into a convenient
> data frame format.
> The shapefile bg11_d00.shp happens to be  the census shapefile for
> Washington DC (you'll also need the corresponding .dbf and .shx in the
same
> directory); I am planning to include a small shapefile in the library in
the
> future.
> PlotPolysOnStaticMap() overlays the corresponding polygons on the map.
>
> Let me know if this works for you,
>
> Markus
>
>
>
>
>
> On Sat, Jan 16, 2010 at 8:35 PM, Patrick Crutcher <pcrutcher@gmail.com
>wrote:
>
>> I have some shapefiles I want to plot over Google Maps tiles. I have
>> polygons, lines and point data. What's the most efficient way to do this?
>> One path might be to use the pkg RgoogleMaps, however, it is still
unclear
>> to me how to do this. I assume using PlotonStaticMap with some
combination
>> of reformatting the shapefile data. Thanks.
>>
>> P.
>>
>
>

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