Hi,


we all know that R is powerful in dealing with graphics.

I am now trying to use R to show some geographic attributes for a
specific geographic area on a graph. For example, if I would like to
generate a graph showing the population densities (in terms of the
intensity of colors) for Illinois State by zip codes. I did some
research; and it seems that package "maptools" is relevant. But I have
the following couple of questions regarding to the application.

1. A State is grouped by several counties, and sometimes we could
further divide it into many areas by zip codes. Will there be any
differences in the shapefiles (.shp)? Do I need to get a specific
shapefile in order to graph on a zip code level?

2. Where can I get this kind of shapefiles?

3. There is another type of file (.dbf) which includes the attributes of
a geographic area. It seems I could put the population densities in it.
But then how could I relate it to the shapefile (.shp)? I mean how to
link a population density to its corresponding zip code area?

4. Finally, how could I use intensity of colors to show the differences
in the population densities?


I would greatly appreciate it if someone could provide me a simple
example. Thanks a lot!


Ningwei


 [[alternative HTML version deleted]]

______________________________________________
R-help@(protected)
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.