1. A computer-implemented method for drawing mapping lines between source and target objects, comprising: displaying a main view that shows one or more source objects, one or more target objects, and mappings between the one or more source objects and the one or more target objects, wherein a mapping line represents each mapping; receiving input that modifies the main view; and in response to receiving the input, determining the slope of each mapping line to be drawn between a source object and a target object, wherein the slope is determined in accordance with: 
 Y1-Y2 
 X1-X2, wherein where X 1 and Y 1 coordinates represent a location of the source object and X 2 and Y 2 coordinates represent a location of the target object; sorting the mapping lines with a mapping strategy using the slope of the mapping lines to sort; and drawing the mapping lines based on the mapping strategy by drawing each mapping line according to the slope of that mapping line wherein each mapping line that has a smaller slope than each of the other mapping lines is drawn before the other mapping lines.