[R-sig-Geo] Finding out in which polygon a point lies

[Dieter Vanderelst]

Dear List,

I've read in a shapefile using the readShapePoly {maptools} function.
This shapefile represents Angola and has different polygons for the
different regions of the country. I also have a set of coordinates
(lat/long). Now want to do two things:

1 - I want to plot the points on the map. Given that both my points
and the shapefile use the same coordinate reference system
(latitude/longitude) and theWGS84 datum, I think I can just use the
function plot(lon,lat). Please correct me I if I'm wrong here.

2 - The second problem is a bit harder. I want to color the polygons
which contain one or more points. How can I check in which polygon
each of the points lie. I found a partial explanation online on how to
do this with the sp package (see
https://stat.ethz.ch/pipermail/r-help/2009-February/187435.html).
However, I haven't been able to reconstruct the method suggested in
this post.

Any thoughts on how to select polygons based on coordinates using
maptools would be most welcome.

Regards,
Dieter