Determining break/border of movement?

Question

A population given inhabiting an area. I can trace every individual and I've got the hypothesis there is a break in distribution like individuals born in the upper half of the area will rarely move to the lower half and vice versa. Tracking each individual how can I determine the line/border which divides the population in a upper and lower half. What's the math or algorithm behind to draw this imaginary line?

Answer 1

Suggest using statistics. Find the line that results in one side has a greater than 50% of the uppers and the other side has a greater than 50% of the lowers. Ideally would sample the entire population or the uppers and lowers. Make a longitude and latitude scatter plot of the locations of the two populations with points coded as to whether it is an upper (like triangles or red) or a lower (like circles or green). Then pick the best line that divides the two. To help with that can use a least means squares fit of each population. That will give two lines and the boarder you want will be between those two.