This function is typically used for the splitting of a paddock into sub-paddocks. To split a polygon:
•Select the object on the map, it’s border will highlight in red.
•Click the Split Polygon button on the Toolbar 
•This will put the map in drawing mode. The idea is to draw a line right through the object to denote the split. Left mouse click to mark the first point outside of the polygon. Then left mouse click again on the opposite side of the polygon. This will display a split line with the areas of the two new sections and the distance the split line is from each node in the object.
•If the split is not exactly right, you can move each end of the line, left mouse click on the node and hold the button down, then drag the node to its new location. The distances from the other nodes and area of the two sections will change as you drag.
•You can move the entire line by holding the mouse pointer on the line until a small white rectangle appears. Then right mouse click holding the button down and drag the line. Again the distances from the other nodes and the area of the two sections will change as you drag.
•Click the Stop Drawing button when finished 
