North Star Line of Sight

Line of Sight is a game mechanic that typically can be worked out gentlemanly between the players. However, if a disagreement arises, NSLoS will be the rule to give a systematic approach that approximates as much as possible the intention behind the 8th edition Line of Sight rules. All unit types and terrain are given a number representing their height which they can use to draw LoS from and other units can use to see them. A higher number can thus draw LoS over any intermediary units with a lower number and can likewise be seen as well.

Size Chart:
0 = Swarms - models of this size never block line of sight or give cover.
1 = Infantry, War Beasts, War Machines, Unique without the Large Target rule.
2 = Cavalry, Monstrous Infantry/Cavalry/Beasts, Chariots, O&G Manglers.
3 = Monsters, all Large Targets

Line of sight is always checked virtually, drawn "base to base". Models see in their front zone. Line of Sight is blocked by models that are equal to or larger than both: the model whose line of sight we are checking and its target.

Line of sight and war machines
Catapults (and similar) can place their template so that the center is over any one unit that is at least partially visible to them. Cannons can choose any point between themselves and a visible target when firing. Over- or under-guessing to shoot at units the cannon does not have line of sight to is not allowed.

Terrain
Hills are size two for each level (so a 2-step hill is size 4) and block sight / give hard cover just like models of that size. Models standing on hills add the hill size to their own size.
Buildings and large rocks always block line of sight completely. The number of levels they are will be labeled at the game table.
Forests do not block line of sight, but soft cover applies to all shots fired through or into (but not out of) forests.
Ruin/rocky patches do not block line of sight, but hard cover applies to all shots fired into (but not through/out of) ruins.
Units standing behind obstacles gain soft (wood) or hard (stone) cover as per the rule book.
Unique pieces of terrain will have information on their limitation to line of sight at the table

Cover from intervening units/terrain
Hard cover is granted when at least 50% of models in target unit are fully or partially obscured by other units/terrain from the shooting model. If the shooter is on a higher level hill, or on the second or above level of a building, then this hard cover modifier is ignored unless the intervening troops are also on the same level of hill or building. Large targets can never claim cover from intervening troops.

Skirmishers
Skirmishers never block line of sight, and are seen in accordance with their size on the chart, but provide cover as per the above rules. The gap between skirmishers is treated as part of the unit when determining if skirmishers give cover to something behind them. Skirmishers formed up for combat block Line of Sight like normal units.