Interactive Polygons

Play with a polygon! Try adding or subtracting points. See different polygons from triangles up.
See the lengths, angles and coordinates, too.
Note: due to computer rounding errors the last digit is not always correct.

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You can draw a rectangle to zoom in, or use the "Zoom" buttons. "Fit" is very useful.


Click on the drawing surface to change the center of drawing. Or zoom out and draw a rectangle.

Fine Adjustments

Draw a small rectangle around a point so you can then position it accurately. Zoom "Fit" to see whole polygon again so you can then zoom in to another point.


Use the "Edit" button to manually edit the coordinates, or to enter new coordinates of your own.

What is Regular, Concave, Complex?

When all angles are equal and all sides are equal it is regular, otherwise it is irregular

When any internal angle is greater than 180° (they would point inwards) then it is concave. (Think: concave has a "cave" in it), otherwise it is convex.

And a complex polygon intersects itself (the boundary crosses over), otherwise it is simple (like most polygons we deal with). Many rules about polygons don't work when they are complex.