Re: [igraph] Maps and Networks

[Lorenzo Isella]

Hi Gary,
And thanks a lot for your suggestion.
This is half a way through what I have in mind: I can put points (and 
probably lines) on a map by specifying their latitude and longitude.
However, I wonder if I can also use "plot" from the igraph to generate a 
network (where the node layout is given in terms of longitude and 
latitude) to overlay on top of the map.
For instance, consider the snippet at the end of the email.
In the first generated pdf, I can actually plot some points on the map 
of Italy, but when I try to do the same using the igraph library, I fail 
to overlay the two plots.
Any suggestion here is really appreciated.
Cheers

Lorenzo



rm(list=ls())

library(igraph)
library(maps)


t <- map("italy", plot=FALSE)


pos1 <- c(16,40.3)
pos2 <- c(12,44)
pos3 <- c(13,42)

pdf("italy.pdf")
plot(t$x, t$y, "l")
points(pos1[1],pos1[2], bg="red", col="red", pch=21)
points(pos2[1],pos2[2], bg="blue", col="blue", pch=21)
points(pos3[1],pos3[2], bg="brown", col="brown", pch=21)


dev.off()



el <- matrix( c("foo", "bar", "bar", "foobar"), nc=2, byrow=TRUE)
g <- graph.edgelist(el)

g <- as.undirected(g)

l <- matrix(ncol=2, nrow=3)

l[1,] <- pos1
l[2,] <- pos2
l[3,] <- pos3



pdf("italy2.pdf")
plot(t$x, t$y, "l")
plot(g, layout=l,
     vertex.label.dist=0.5,vertex.label=NA, vertex.size=5)


dev.off()







On 27/04/11 18:11, Gary Weissman wrote:
> Hi Lorenzo,
>
> If I understand your question correctly, then you can use the maps library in 
> R.  There is a Stack Overflow thread which gives a little more detail here:
>
> http://stackoverflow.com/questions/3951734/network-graph-and-us-map-in-r
>
> Best,
> Gary
>
>
>
> On Apr 27, 2011, at 12:00 PM, address@hidden wrote:
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> >    1. Maps and Networks (Lorenzo Isella)
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> > ----------------------------------------------------------------------
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> > Message: 1
> > Date: Wed, 27 Apr 2011 16:01:44 +0200
> > From: Lorenzo Isella<address@hidden>
> > To: address@hidden
> > Subject: [igraph] Maps and Networks
> > Message-ID:<address@hidden>
> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> >
> > Dear All,
> > A question on the visualization side of network; from time to time we
> > all happen to see geographical maps (e.g. air transportation) with a
> > network overlaid upon them (e.g. links between London, Paris, Berlin and
> > Rome, just to consider Europe only).
> > I tend to use igraph under R and ggplot2 for statistical visualization,
> > but how can one generate some good looking visualizations mainly by
> > scripting only?
> > As of now, I would not know even where I can fetch the maps (let's say
> > Europe) for the task, let alone overlay a network upon them.
> > Does anyone have experience with this kind of visualizations?
> > A self-contained example even with fake data would help me a lot.
> > Best Regards
> >
> > Lorenzo
> >
> >
> >
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> > End of igraph-help Digest, Vol 57, Issue 18
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> --
> Gary Weissman
> http://www.babelgraph.org/
> address@hidden