[R] drawing filled countries according to data using map('world')?

[Jens Hainmueller]

Hello,

I am looking for somebody who has experience with the map library (Becker
and Wilks 1993) and might be able to help me with the following problem:

Using the 'world' database I would like to draw filled countries in a world
map so that the filling colors of each country corresponds to the value of a
policy variable X at time t (the goal is to visualize a policy diffusion
pattern over time using different maps for t=1985, 1990, etc.).

In their explanatory note, Becker and Wilks show how to accomplish this with
the 'states' database, for filling US states with color according to the
republican vote in 1900.

> state.names <- unix(’tr "[A-Z]" "[a-z]"’, state.name)
> map.states <- unix(’sed "s/:.*//"’, map(names=T, plot=F))
> state.to.map <- match(map.states, state.names)
> color <- votes.repub[state.to.map, votes.year == 1900] / 100
> map(’state’, fill=T, col=color)
> map(’state’, add=T)

"The first expression changes uppercase to lowercase in the standard S
dataset giving state names,
so that these can be compared with the names returned by map. Next the
complete set of state
polygon names is requested (using map(names=T,plot=F); the default database
is
’state’) and the trailing portions (from the '':’’ onwards) are removed so
that we have a list of
the state for which each polygon is a part or the whole. Then we create
state.to.map that
gives the translation from the ordering of the states known to S
(alphabetical) to the ordering
known to the mapping mechanism. By using this vector, as in the next
expression, all the pieces
of a state will be colored the same color. The state.to.map vector is a
useful one to keep
around, for it will work in any context where the ordering of the state data
is as here. Notice that
unless such a vector is being reused, it will usually be the case that there
will be a step like this
one, finding the translation between the ordering for the regions in your
data and the ordering
according to map. In general, the translation will have to be computed each
time the set of
selected polygons changes."

My question then is, how to compute a similar procedure using the 'world'
database. Specifically, how can I access the country names in the 'world'
database to accomplish the translation to the country names in my dataset?
Is there any way to unpack the 'world' database to do the matching in an
external program? And does anybody now of other (more recent) world maps
that I could use?

Thanks very much!

Best,
Jens