Contour Plots

Hello all.

I'm confused a bit about contour plots.  After reading the help at
"?contour", it seems as though the contour plot is for 3D plots (x,y, and
z).  My data is in the form of grid coordinates (x,y), and I want to see a
contour plot of the data so that I can tell where most observations lie. 
My question is simple but still evasive.

Say my data is called places.  One column is X and another is Y.  Or,

                  places$X          places$Y

Coordinate 1          32               50
Coordinate 2          15               33
Coordinate 3          28               20
etc

How do I get R to do the contour plot with no third "z" coordinate?

Thanks.

Do all you can with what you have in the time you have in the place you are!

-Nkosi Johnson, 12-year old African hero