GPS tracking and graph updating

Hi

Im working on a GUI, whose purpose is to develop a system to measure distance between two work stations using GPS coordinate system.

pl guide me how can i measure distance if i get 4 GPS coordinates , two of the existing syste and two from other remote system.

moreover im drawing these coordinates on a graph, the problem is that after sometime when the points are updated, the graph shows the points in a straight line, since there is not much distance not more than 50 m.

kindly share with me a technique so that the distinguished points are shown in graph instaed of a jumbled set of points like a straight line.