There is no built-in series that is suitable for display of arbitrary closed contours.
You can draw the contour with custom painting. Please take a look at the following examples in our Windows forms demo application:
All Examples > Custom Painting > ...
All Examples > Coordinate Transformations > ...
Geometry painted like this always appears on top of the chart. The upcoming version of Nevron Chart has a "Custom Series" with the help of which you'll be able to set specific depth order of the geometry in relation to other series.
Best Regards,
Nevron Support Team