Axes are used in several different kinds of plots to provide quantitative indexes for the scale of each plot direction. Gnumeric uses four different kinds of axes. Category axes do not provide a quantitative scale but merely distinguish each different category by providing space for the values of the category along the axis. Continuous axes provide a quantitative measure of each value based on the projection of that value onto the axis. Radial axes are used in radar plots and are continuous axes which radiate from a central point. Circular axes have not yet been implemented.
Line, column and area charts use a category axis to separate the categories along the horizontal direction and a continuous axis to distinguish values in the vertical direction. Bar charts reverse these two axes. XY scatter plots and bubble plots use two continuous axes, one in the horizontal direction, the X-axis, and one in the vertical direction, the Y-axis. Radar plots use three or more continuous axes radiating from a central point. Pie and Ring plots do not use any axes.
Category axes distinguish the different categories of each value in a category series such as the series in line, bar, column and area plots.
The Bounds tab allows the user to override the automatic configuration of axis tick marks and labels. Each of the three choices can be over-ridden by deselecting the check box on the left. The check boxes can be deselected by placing the mouse pointer over the check box and clicking with the primary mouse button. When a check box is unselected, the entry box will become active allowing the user to input a different value than the default. The first check box controls the number of tick marks, allowing tick marks to appear after the integer number of categories shown. The second check box controls the number of labels displayed, allowing a regular number of category labels to be skipped. The third check box controls the placement of the orthogonal axis relative to the category axis.
The Style tab allows the user to configure the line style of the axis, including the color and thickness of the line. The drop down button labeled Color can be clicked to expose the color picker panel which allows the user to select a new color either simply by clicking on an icon or by using the color picker wheel. The size spin button allows a user to change the thickness of the axis by typing a new number in the text box or by clicking on the arrows. A value of '-1' in this box will cause the axis not to be drawn.
The Font tab allows the user to configure the font used to label the separate categories. The font configuration is performed in the same way as the font configuration for titles and axis labels which was explained in Section 10.4.2 ― Titles and Axis Labels.
The Details tab allows a user to configure other aspects of the axis.
The Position of the axis is placed in the Low position by default. This can be altered by pressing the radio button in front of the High label which will move the internal button and will alter the position of the axis, moving it either to the top of the graph for horizontal axes, or to the right of the graph for vertical axes.
The Mapping of the axis can be changed simply by clicking on the check box. This will cause a check mark to appear in the box and will invert the axis so that the order of the categories will become reversed.
The Major ticks displayed on the axis can be altered. The labels shown in the plot can be hidden by unchecking the check box in front of the 'Show Labels' text by placing the mouse cursor over the box and clicking with the primary mouse button. The ticks on the axis can be hidden or can be displayed on the outside of the graph, or on the inside of the graph, or on both sides depending on which of the two boxes are checked.
The Minor ticks do not currently have any effect for category axes.
Continuous axes are configured in much the same way as category axes except for some minor differences.
The Bounds tab allow users to configure the limits and intervals of a continuous axis. The meaning of the values for Major Ticks and Minor Ticks depends on the type of continuous axes:
The Major Ticks value gives the distance between major ticks and the Minor Ticks value the distance between minor ticks.
The Major Ticks value gives the number of decades (powers of 10) between major ticks. The Minor Ticks value gives the number of minor ticks between major ticks.
If the Major Ticks value is N, then the Minor Ticks value can be 0, N−1, or 9N−1.
The Style tab changes the linear style of the axis in the same way as it acted on category axes. The explanation given in Section 10.4.4.1 ― Category Axes apply equally well to continuous axes.
The Font tab also allows users to configure the font used in the numeric markers along the axis. Selecting the font for a continuous axis works in the same way as for a category axis as was explained in Section 10.4.4.1 ― Category Axes.
The Details tab has two small differences compared to category axes. The mapping of the axis can be altered from a linear scale to a logarithmic scale by clicking on the drop down box and dragging to the entry labeled Log. The minor ticks, whose size was configured in the Bounds tab, are displayed for continuous axes unlike for categorical axes.
The Format tab allow users to configure the numeric type of the elements on a continuous axis. This configuration parallels the configuration of the numeric type of a worksheet cell as explained in Section 5.10.1 ― Number Formatting Tab.