Mechanics for Map Design

Hello, everyone! It’s time again for a Combat Cartography article! This month, I’m going to talk about the rules elements you can quickly incorporate into making exciting and dynamic combat maps.

Hard Corners

If the corner of a square on the combat grid contains an object, that square is what I call a “hard corner.” A character can never pass through a hard corner. When we talk about sizes and placement in next month’s article, hard corners will be essential considerations since they’ll affect the shortest possible routes characters will be able to move through an environment.


Cover, in its broadest sense, is how much of a target a combatant can’t see. Naturally, an enemy you can’t see as well will be harder to hit.

Measuring Cover

To measure cover between an attacker and a target, find the corner of the attacker’s square closest to the target, and imagine a line from that corner to each of the closest three corners of the target’s square.

If two corners are an equal distance from the target, instead imagine lines from each of those corners to the target, plus an extra line in the center.

There are four degrees of cover.

A target has no cover when there is nothing between the attacker and the target. Cover has no bearing on an attack in this situation.

A target has half cover when only one of these imaginary lines is broken. A target with half cover gets +2 to AC and Dexterity saving throws.

A target has three-quarters cover when two of these three imaginary lines are broken. A target with three-quarters cover gets +5 to AC and Dexterity saving throws.

A target has total cover when all three of these imaginary lines are broken. You can’t target a creature or object with total cover.


Finally, if any of these three sight lines pass through a hard corner, consider that sight line broken.


Typical examples of partial cover can include obscuring foliage like trees, structural elements such as columns and walls, and fences and grates(which block movement but won’t grant total cover!).


Cover is an often-overlooked aspect of a battlefield, but it can be used to subtly direct ranged combatants(or reduce their control of a combat encounter). In fights where you don’t want an emphasis on ranged combat, include sporadic sources of cover to break up the largest lines of sight. In combat scenes where you’d like ranged combatants to be most important, try to avoid adding too many sources of cover to your battle maps as they’ll create stalemates in which both sides of a fight will typically hide.

Difficult Terrain

Difficult terrain is terrain which you can’t reliably cross at an average pace. This can be because it’s unstable, covered in sharp bits, slippery, or any justification you like. Entering any square of difficult terrain costs an extra 5 feet of movement, and exiting it does not cost any extra movement. A square is considered difficult terrain only if its center is considered difficult terrain. You can also mark difficult terrain squares with a triangle in the corner to help communicate it to your players.


Typical examples of difficult terrain include discarded rubble, thick vines, or shifting ground such as loose sand or large piles of coins(though if you’re in a combat encounter with something on top of a large pile of coins, I’d imagine you’ve got other trouble to handle!)


Difficult terrain can shape the paths that combatants choose when crossing a battle map. Place difficult terrain in areas that you want combatants to either hesitate to enter or find difficult to leave, such as areas with little cover from ranged attacks or areas where melee combatants can get a jump on targets more comfortable with fights at a range.


Half-walls are a special environmental feature. The most common examples are waist-high fences or small barricades, which are typically placed to make it inconvenient(but not impossible) to cross an area. A creature behind an adjacent half-wall about half of its height benefits from half cover while standing and three-quarters cover while prone.


Hazards are my blanket term for any additional terrain feature which has a mechanical effect when a character enters, leaves or stays in an area. Hazards can vary significantly depending on your campaign’s combat situations, and are the most flexible element of a battle map.


Hazards can come in an extensive variety, so here are a few bulleted ones which I’ve used in recent memory.

  • Leaking steam pipes which scald passers-by(dealing 2d6 Fire damage whenever a character an area within 10 feet of the pipe).
  • Large, continuously-rotating gears which move anyone standing on them clockwise by 1 square.
  • Slippery patches of ice which, if a character ends their turn on them, require a moderate DC dexterity save to avoid falling prone.
  • Areas in a war zone where errant arrows frequently rain down, which I usually use in situations where there would be too many unimportant combatants to track individually.
  • Lava, whose mechanics are best represented using Fire and Brimstone, a free PDF which offers a comprehensive approach to volcanic adventuring.


Use hazards sparingly to thematically compliment an area in a combat encounter. I typically like to use them to keep combatants moving in some capacity, either (slightly) punishing combatants for standing still or passively adjusting the battlefield either by moving characters or by somehow changing the shape of a map.


Drops are changes in elevation of stable terrain. A drop occurs between two squares if either of the following conditions is met:

  • A square is 10 feet or more below an adjacent square without a gradual slope(such as stairs or sloping ground).
  • A square contains a hazard or difficult terrain(as described above)

A creature can cross a drop, either willingly or unwillingly, from the higher square to the lower square without expending any extra movement, immediately falling the vertical distance of the drop. A creature being forced to cross a drop may make a Dexterity saving throw(the DC of which should be up to you as a storyteller to decide; I typically like to use a DC of around 15). On a success, instead of being forced across the drop, the creature falls prone and the forced movement ends. A prone creature can’t make this saving throw.

For every 10 feet a creature falls, it takes 1d6 bludgeoning damage, up to a maximum of 20d6 at 200 feet or greater. Spells such as feather fall and cat’s grace specifically can reduce this damage, as can certain class features.


Drops are a funny feature in your maps – at earlier levels, even a 10-foot drop can prove dangerous, and strongly dictates how a creature navigates their environment. At these levels, you can use drops as walls which do not provide cover – ranged attackers can use a drop like this for protection from melee combatants without the restrictions that aiming around cover would entail. However, drops become much less significant at higher levels – creatures with large numbers of hit points, effects to mitigate falls, or damage resistances become much more common, and they may gladly hop over drops to engage with a foe more quickly. When designing maps with drops at higher levels, consider them to be more like one-way passages. A creature may willingly fall down a drop to get into(or out of) a fight, but going back up will quickly prove more difficult than going down.


With this vocabulary of map terms, you can quickly add new mechanical spice to your combat encounter. Just remember: like any spice, a little can go a long way. Try to avoid overwhelming your players with too many mechanical details at once, but keep these mechanics in mind for ways to design dynamic maps to engage your players.

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