Mapping Concepts


LMB: left mouse button click, RMB: right mouse button click


Vertices are the joins between Lines, and the corners between walls.

  • Press v in the 2D view to enter Vertices edit mode
  • LMB while hovering over a Linedef inserts a single vertex at the cursor position
  • RMB inserts a vertex in line drawing mode, keep adding vertices with RMB until you close the polygon


Linedefs divide the map into sectors, and they are also used to trigger actions.

Press l in the 2D view to enter Linedef edit mode.


A linedef also has a front and a back. You can tell the front of a Linedef by the direction of the protruding pin in the middle of the Linedef.


this linedef front is facing down


A sector is an area defined by multiple Linedefs.

Press s in the 2D view to enter Sector edit mode.



Things represent players, monsters, pick-ups, obstacles, decorations, player start positions and teleport landing sites.

Press t in the 2D view to enter Things edit mode. space or ins inserts a new thing at the cursor position.


Multiple selections

While in the 2D view, you can select Vertices, Linedefs, Sectors and Things by:

  • Clicking an item to select/deselect it
  • Drag-select multiple items to include/exclude them in the selection
  • Hold shift to prevent moving things around when making a selection

Switching between Vertices, Linedefs and Sectors will preserve any selections as much as possible.


Press ` (back quote) in the 2D view to deselect everything.


You can scale and rotate selected Sectors, Linedefs and Vertices.


Click on Edit -> Scale Objects or press F3 to show the scale dialog.


Four inner most vertices are selected


Scaling the vertices by 50% on the x-axis



Click on Edit -> Rotate Object or press F4 to show the rotate dialog.


Four inner most vertices are selected


Rotating the vertices by 45 degrees




A Sidedef refers to the texture data for a Linedef, it can have lower, middle and upper textures.

The relation of the sidedefs are best illustrated with these poorly-matched textures:


Lower texture is COMPBLUE, middle is MIDGRATE, and upper texture is BRICK10

To change the sidedefs

  • Switch to 2D mode
  • Enter Linedef mode (l)
  • Select one (or more) linedefs
  • Click the “Front sidedef” texture button to open the texture browser
  • (optionally) Press tab to switch to 3D view for a live preview
  • Select a texture in the browser window

Floor / ceiling textures

Enter Sector editing mode and select the sector to change:


Click the texture buttons to open the texture browser:


You can enter the 3D view to see a preview of the texture changes: