How do remove the border around a core-plot graph

You should be able to nil out the borderLineStyle on the graph's plotArea to remove the border:

graph.plotAreaFrame.borderLineStyle = nil;    // don't draw a border

You could also create your own theme, using the ones in the framework as examples, and simply not set the borderLineStyle in that.

OK I found out how to do it - quite simple really!

CPLineStyle *borderLineStyle = [CPLineStyle lineStyle];
borderLineStyle.lineColor = [CPColor whiteColor];
borderLineStyle.lineWidth = 1.0;

graph.plotArea.borderLineStyle = borderLineStyle;

where graph is your graph object - the reason I had a border in the first place was because I used CPPlainWhiteTheme.

Hope this helps others - is there a better way?

You can set any line style to nil. This will cause the line to not be drawn at all.