How to plot contours on a map with ggplot2 when data is on an irregular grid?
Sorry for the wall of text, but I explain the question, include the data, and provide some code :) QUESTION: I have some climate data that I want to plot using R. I am working with data that is on an irregular, 277x349 grid, where (x=longitude, y=latitude, z=observation). Say z is a measure of pressure (500 hPa height (m)). I tried to plot contours (or isobars) on top of a map using the package ggplot2, but I am having some trouble due to the structure of the data. The data comes from a regular, evenly spaced out 277x349 grid on a Lambert conformal projection, and for each grid point we have