Think of a board game, any board game. I'm going to say Sorry! Now, think of what the board looks like. Other than possibly changing the theme or updating to more modern images, most boards stay the same. Boardwalk is always next to Go in Monopoly, the starting star in Scrabble is always in the middle of the board, and the cities in Ticket to Ride are always in their correct location.
Can you imagine a game board that isn't always the same? During one game there is a river going right down the middle of the board. During the next game, using the same board, you are now faced with mountains to cross?
One of the fun things about some hobby board games is that the board itself may not be the same each time you play. Some mainstream games are picking up on this mechanic as well. The U-build series of games like Monopoly and Mouse Trap are some current examples.
I like modular boards because they add a lot of re-playability to games and they allow one board to fit multiple scenarios. This is useful in war games like "Commands and Colors." It allows people to play more than just one battle on the same board. It wasn't until I started writing about this mechanic that I realized just how many of my games are modular. It was funny to go through my list of games and see how many fit this mechanic.
Hallmarks of Modular Board Games
The hallmark of modular board games is that the board changes from game to game. (Insert isn't that obvious joke here.) How the board changes varies.
One Board - Multiple Overlays
Overlays are the things that can be put on the board to change it around. Some examples of overlays are tiles or cards. The rule book may come with specific directions for the set-up, or it may be up to the players to chose where the overlays are placed. The board itself doesn't change, but how it looks from game to game will.
Memoir '44 is a great example of one board making use of multiple overlays. The base game comes with a double sided board and lots of different terrain tiles. Players can play the board as is or add the terrain tiles.
These terrain tiles allow the game to simulate different battles from WWII. The terrain tiles affect movement and attack ability. The affect may be advantageous to you are a pain in the rear.
Variable Board Placement
Another way to change things up with modular boards is to randomize board placement. This usually means that the board is made of multiple pieces that are changed around from game to game. Players change their strategy from game to game since things are never in the same location.
In "Sid Meier's Civilization: The Board Game" there are multiple map tiles that are randomly placed each game. As an extra challenge all but the home map tiles are placed face down at the beginning of the game. Players explore to discover the map.
Another variable for this type is to not use all the game pieces at one time. In games like Descent and Dungeons and Dragons: Castle Ravenloft players place the board tiles as they discover and move into new locations. You reveal the dungeons as you explore it, never knowing what dangers or treasures may lurk around the next corner.
Variable board placement does not always mean players don't know what the board looks like from the beginning of the game. Heroscape boards are built before the game starts and players know what it looks like even before they start playing. Again players can use the scenarios in the rule but or create their own map.