RadChart has been replaced by RadHtmlChart, Telerik's client-side charting component. If you are considering RadChart for new development, examine the RadHtmlChart documentation and online demos first to see if it will fit your development needs. If you are already using RadChart in your projects, you can migrate to RadHtmlChart by following these articles: Migrating Series, Migrating Axes, Migrating Date Axes, Migrating Databinding, Features parity. Support for RadChart is discontinued as of Q3 2014, but the control will remain in the assembly so it can still be used. We encourage you to use RadHtmlChart for new development.
Spline charts allow you to take a limited set of known data points and approximate intervening values. In practice you define a series of chart items with X/Y values and RadChart does the rest.
To create a simple vertical Spline Chart set the SeriesOrientation property to Vertical. Set the RadChart DefaultType property or ChartSeries.Type to Spline. Create a series and add chart items with Y or X and Y values.
To create a simple horizontal Spline Chart set the SeriesOrientation property to Horizontal. Set the RadChart DefaultType property or ChartSeries.Type to Spline. Create a series and add 3 or more chart items with X and Y values.
Another example showing the same Y data points as above, but with no X values defined displays an automatic even progression over the X axis.