[R] how to make a contour plot using data in long format

[Dieter Menne]

Maria Wang <mariayzw <at> hotmail.com> writes:

> 
> There is a dataset with Latitude Longitude information and corresponding 
> value shaped like this:
> Lati                     Longi                  Value
> 18.0001             -159.6667             123
> 18.0023             -159.6665             124
> I want to use this data to make a filled contour map imposed on an USA map. 
....

Best use package geoR. There are also some examples in MASS (chapter 14).

Dieter