# Simple polygon > [[PORTAL_Graph_theory|Graph theory]] spine. ## Microsims — three.js <div class="microsim-player"> <iframe src="https://wikitube-3d-microsims.netlify.app/Simple_polygon_microsim.html" width="100%" height="520" frameborder="0" loading="lazy" sandbox="allow-scripts allow-same-origin" title="Simple polygon — three.js microsim"></iframe> </div> <p class="wt-pending"><strong>Note:</strong> staged, awaiting CDN deploy.</p> A simple polygon is a closed shape traced by a sequence of straight line segments that do not cross each other — the boundary forms a single loop with no self-intersections, cleanly separating the plane into an inside and an outside. Triangles, squares, and any hand-drawn non-self-crossing outline are simple polygons; a figure-eight shape is not. ## Overview This build lets a viewer construct and manipulate polygons directly and see the simple/non-simple distinction update live as vertices move and edges begin or stop crossing. The condition matters throughout computational geometry and [[Graph_theory|graph theory]]: algorithms for triangulating a shape, computing its area, or testing whether a point lies inside it all assume a simple polygon as input, and a polygon's boundary can itself be read as a cycle in a planar graph. **On the spine:** [[Graph_theory]] · [[Simplex]] · [[Surface_(topology)]]. ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Simple_polygon) : [Wikitube](https://en.wikitube.io/wiki/Simple_polygon) --- *Repopulated 2026-08-05 · existing three.js asset renamed + wired, Wikipedia-sourced overview · 0 deletions.*