Zircon is a map with two lanes and a mid-point connecting them. The key contention points are marked with X's.
The Colours of the lines indicate who typically has an advantage in that lane, losing in your advantage lane is not great because your opponent will have an easier time controlling both lanes if that happens. Why are these lanes advantage lanes? In the bottom lane Red will have an advantage because they have 2 builders compared to Blue's one, similarly, on the top lane Blue has the advantage because they have a numbers advantage.
EDIT: Forgot to put it on the map but mid (the purple line) is also a key contention point since it allows you to transfer troops from your advantage side to your disadvantage side.