There is a `PolygonAnnotation` class that uses a collection of points. Complex paths are not supported. Also note that the annotation classes are not optimized for performance (like the series), so 260 000 points may make the plot very slow.

I tried to improve the comments on the methods a little bit.

The `DrawClippedLineSegments` extension method on `IRenderContext` does the same thing as `IRenderContext.DrawLineSegments`, but applies a clipping rectangle to the output. The clipping is done by OxyPlot, not by the graphics system implemented in the render context. 

The `DrawLineSegments` method draws line segments from point 0 to 1, point 2 to 3 and so on.

I think `rectangle.DrawClippedLineSegments` should be replaced by `renderContext.DrawClippedLineSegments` in your post.

I am not sure what it should be called...
http://en.wikipedia.org/wiki/Software_design_pattern
No abstract creational patterns used, I think. It's just a portable library used by all the platform specific example browsers. Depends on reflection to work!

It's work in progress, please contribute! :-)

I think subplots would be a great feature, but it requires some architecture refactoring of the `PlotView`s.
I think each subplot should be defined by one PlotModel (yes, it can contain multiple series) and then you compose the view by a grid of subplots defined by column, row, colspan and rowspan.

https://github.com/oxyplot/oxyplot/issues/55

Good idea! I have added issue #342!

Xamarin.Forms should be supported, and updated to latest Xamarin.Forms version in the latest pre-release OxyPlot.Xamarin.Forms NuGet package.

could this be related to issue #288? If not, create some code to reproduce the problem and create a new issue!

HeatMapSeries?