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Isometric projection represents three-dimensional objects in two dimensions where the angles between the projection of the x, y, and z axes are equal (120 degrees apart). In isometric paper, vertical lines remain completely perpendicular to the baseline, while lateral axes project upward at exactly 30 degrees from the horizontal.
Carpenters use isometric paper to draft complex mortise-and-tenon joints, cabinetry carcasses, and timber frame bents. Because parallel lines never converge toward a horizon, dimensions can be measured directly along any of the three primary axes with a standard ruler.
Dungeon masters and mapmakers use equilateral triangular grids to illustrate multi-level isometric dungeons, castle keeps, and vertical encounters for games like D&D and Pathfinder.