Drawing directed graphs on the US map

I was wondering how can I draw a directed line with has (latitude, longitude) coordinates? I am looking for directed version of "linem" function.

[Walter Roberson]

I would say you are looking for the mapping version of the annotate() function.

[Taha]

@Walter: how can you get the pixel coordinates of a (latitude, longitude) coordinates? If I know this, I can use the annotate() function to draw an arrow.