Specifying Width and Height
You can specify how much of a battle map you are looking at at any given time by specifying the number of cells wide and number of cells high you'd like to be looking at. (Default 10x10)
Example
https://otfbm.io/5x2/
Panning the map
You can also move what part of the map you are looking at around by prefixing the width and height values with a map cell the defines the top left corner of the view.
Example
The following will display a 5 cell wide by 2 cell high view starting at m3
https://otfbm.io/m3:5x2/
Alternate syntax
Another, simpler syntax makes it possible to display a viewport by a given top left cell and bottom right cell.
Example
The following will display a 5x2 grid starting in the cell c3
https://otfbm.io/c3:g4/