I wondered about a lot of this a bit early on, then I did some more research... Using the PHB and DMG, here is what I have come up with: For cones, p204 of the PHB says, "A cone's width at a given point along its length is equal to that point's distance from the point of origin." Thus, a 15' cone, cannot be wider than 15' at its widest point (the end of the cone). As such, the angle for a cone is not 90º, it must be between 55º and 60º, as shown below: Remember (also in the PHB, p204 under Cone), a cone's point of origin (usually the caster) is not included in the effect. Additionally, the guidance given, as far as what squares are affected then, is on p204 of the PHB, in the paragraph immediately preceding Cone, "A spell's effect expands in straight lines from the point of origin. If no unblocked straight line extends from the point of origin to a location within the area of effect, that location isn't included in the spell's area." In this case, you can use the ruler tool, and it centers on a given square. If you take it out to the edges of the (in this case, purple) cone, the ruler arrow will be covered from point of origin (caster) to the corner of the purple cone in all the squares marked in the red overlay. The only question becomes, why are those corners included in the spell effect? Well, using the previously referenced point preceding the Cone section on p204, the center of that square falls within the cone, thus it is affected. If we used the more traditional 90º, it would appear as such: The areas affected are significantly more than 55º-60º, and it violates the rule that a cone's width (at a given point) is equal to its length (at the same point) from the point of origin. Cones, I think, are the hardest, but circles/spheres/cylinders have been done incorrectly also, insofar as where 5e is concerned (not with this script, it works perfectly, but the D&D community in general). Most templates have a crazy look to them, as to what is covered under a sphere. For example, this is how a traditional template for a 20' fireball appears: I've never thought anything of it, until I read in the DMG (p251) under the section for Areas of Effect, "If an area of effect is circular and covers at least half a square, it affects that square." If you look at how a circle actually appears when drawn out, it looks like this (deleted the fireball overlay, but kept the red border to show): The areas in blue are areas which should be covered under the area of effect for a circular area, which are not based upon "standard" template methodology. That's an accumulation of 8 more squares (at a 20' radius) beyond what previously occurred. I'm not saying this is a bad thing, nor am I saying it is a good thing. In truth, I'm merely mentioning these discrepancies because if you do plan on making overlays to work where you draw out the shape, and it highlights areas of effect (like the blue or red "overlays" above), accuracy in why and which squares are affected, is needed.