I often see people ask whether it is possible to play 4e without a battlemat. Most responses to this questions are to say it isn't possible. Fourth Edition is very tactically oriented. Many powers involve sliding, pushing, pulling, and shifting characters around the battlefield. Combat is supposed to involve fields with unusual terrain to give an added dimension to combat.
Well, I'm here to tell you that it is possible to play 4e without a battlemat. However, it requires four things:
First, you need a DM with a very good sense of spatial awareness. Without a visual representation of the battlefield, you, the DM, need to keep the relative position of all the PCs and NPCs in your head. You need to be able to describe the field with enough detail so the players understand what's going on and what their options are. Without a mat, you bear most of the burden of narration and evoking an immediacy to the battle. Not all DMs are up to this task, so think long and hard about whether you'll be able to keep track of 5 or more PCs and and equal number of NPCs (including all the minions!)
Second, you need very easy-going players. A picture is worth a thousand words and withut a map, you don't have pictures and you don't want your DM giving you extensive narration every time combat begins. This means the players necessarily are going to be given incomplete information. Players can supplement this by asking questions, but even then, there will be confusion and miscommunication. Players without a mat have to be patient and they have to roll with the inevitable inequities that comes when a DM has to keep track of the entire battle mentally.
Third, you need cooperative character building. 4e classes are built for battlemats. Many classes -- particularly swordmages and warlords -- work best when players can work the battle map like a chessboard. Without a map, these characters could be rendered useless, or they could be rendered all powerful, depending on how the DM translates the class' powers into the new format. The players and DM should work together to make sure all the characters will be useful and more or less balanced with one another. If a PC appears to be overpowered, the player has to understand that the DM may begin to tone down those powers so everyone can contribute equally. If a PC appears to be underpowered, the DM should allow more extensive retraining to the PC can be a more effective part of the team.
Fourth, you need to learn SARN-FU. SARN-FU is an acronym for the system I developed to translate 4e into mapless playing. It works as follows:
Rather than measuring the distance between any two objects or creatures in squares, measure that distance narratively, with the following "Positional Relationships" (PRs): Squeezed, Adjacent, Reachable, Near, Far, and Unreachable. The relationship between any two creatures can be described in these terms. Each of these Here's what each of those terms means:
Squeezed (0) means the two characters share the same space.
Adjacent (1) means the two characters are within arm's length of one another. Adjacent characters can attack one another with melee attacks. If a medium or smaller character has two or more adjacent enemies, it is flanked. If a large or larger character has four or more adjacent enemies, it is flanked.
Reachable (2) means the character is close, but just beyond melee reach. A reachable character can be attacked with reach weapons or if the attacker has reach. An attacker with threatening reach is considered adjacent to characters to which it is reachable for purposes of determining if the target is flanked.
Near (5) means the character is close enough for most ranged combat, but is too far away for most melee combat.
Far (10) means the character is so far away that ranged attacks incur a penalty for being beyond the character's close range attacks.
Unreachable (20) means the character can be seen, but not attacked, even with the character's longest-ranged attacks.
Translating Powers. So what do you do with this? Quite simply, if one character is attacking another, the range of the attack must equal or exceed tohe value of the PR describing their relationship. So if my character has an attack with a range of Ranged 5, I can attack characters that are squeezed, adjacent, reachable and near, but not those that are far or unreachable. For area attacks, the player can choose how close to place the origin of a burst or blast to any target, but the DM must then determine whether other targets would also be within the burst or blast radius.
Movement, Forced or Free. Movement works similarly. In order to change the PR between two characters, subtract (if you move closer) or add (if you move away) to the PR value. Then round the new number upwards to the next PR. So to move from Far to Adjacent, a character needs to move 9 (usually necessitating two move actions). If the PR changes, the DM then has to determine how this affects the mover's PR with respect to all other characters. Forced movement can allow one character to alter the PR between two other characters.
Opportunity Attacks. Without a battlemat, it is very hard to determine when someone moves through another person's threatened squares. Whenever someone ceases to be adjacent to a target character (with any movement other than a teleport or shift), all other characters adjacent to the target get an opportunity attack against the mover. While this is very different from standard combat, it makes a good rule of thumb that causes about as many opportunity attacks as in combat with a mat.
It takes a while to get used to the new flavor of combat and playing without a mat. But for some groups, this is more free-form than using miniatures. It requires a group with a lot of trust, and with people who would get upset with the inevitable arbitrariness of the DM having to calculate all distances mentally.
Edited to add (07/01/2010): Enclosed is a card you can print out and place on your game table to help the DM and players to remember the easy rules of SARN-FU:
Enjoy and let me know if you use these rules!