Core Plot - X-Axis moving position when plotting less points

Question

I have a strange problem where my x-axis moves down the plot area when I'm plotting less points. My graph has 2 lines plotted - 1 for previous year and 1 for current year values. My original graph always plotted 12 points for both lines, regardless of which month we are in and this works fine. I have now changed my app so that the current year line only plots points upto the current month. E.g. we are in May so I only plot 5 points. When I do this the x-axis moves down the plot area so that it is detached from the y-axis and the labels are hidden - see screenshots :

Why would simply reducing the number of plot points change the x-axis position? I'm using Core Plot 1.1 (static library) and Xcode 4.6.2.

Answer 1

The yRange of the plot space changed so the point where the x-axis crosses the y-axis is now too close to the bottom edge of the graph. You have two options:

• Ensure the yRange always puts the crossing point (the "orthogonal coordinate") far enough from the edge that the labels and title remain visible.

• Use the axisConstraints to position the axis a fixed distance from the edge of the graph. This will let the crossing point float along the y-axis.

Answer 2

The plotting library changes the x-axis position because generally core plot take the minimum and maximum range among the values of y axis. You when you provide only 5 points then the lowest value is taken from y axis values and there for x- axis position while when you were providing all 12 months values the lowest value of the rest of the month were 0 and therefore x-axis was at zero. You can change the maximum and minimum values for the y range in core plot.