Algorithm for Latitude-Long

[Jacinda M. Barbehenn]

I have a data set of the midpoints of counties based on latitude and
longitude coordinates.  With this data set I want to create a matrix that
lists the distances between counties.  However, to use latitude and longitude
data, I need an algorithm that will correct for the longitude distances.
Does anyone know of an algorithm that can do this?


-jacinda barbehenn
 USACERL/UI GISLAB 
 mountz at gis.uiuc.edu