Line Plots

Line plots present the numeric values of categorical data with the data values of each series connected by a line. Sequential data values are considered to belong to different categories and are plotted along the horizontal (X) axis at equally spaced intervals. The data values from different series are assigned to these categories based on the position of the value in the series, for example, the second data value taken from each series all share one category. The data values are plotted along the vertical (Y) axis according to their numeric value and the particular sub-type chosen for the line plot.

Line plot sub-types provide three options for relating the values from different data series. The first sub-type plots each series independently with the data value determining the vertical distance between each point and the horizontal axis. The second sub-type plots the series stacked on each other in a cumulative fashion with the data value of each series determining the vertical distance from the point to the sum of the values in all the previous series. For example, if the first series starts with values {3.9, 4.2, ...}, the second series with values {1.2, 3.5, ...}, and the third series with values {3.1, 1.9, ...}, then the point value for the second element of the third series will be plotted at 9.6 (9.6=4.2+3.5+1.9) along the vertical axis. The third sub-type plots each series based on the proportional contribution of the value to the total of all values in that category. Using the example above, the three values would be plotted at 0.4375, 0.8020, and 1 because the intervals between zero and each of these numbers is 0.4375=4.2/(4.2+3.5+1.9) for the first, 0.3645...=3.5/(4.2+3.5+1.9) for the second, and 0.1979...=1.9/(4.2+3.5+1.9) for the third, although, by default, these numbers are presented as percentages on the vertical (Y) axis.

Two styles are available by default for line plots. In the first no markers are placed on the value of the point whereas in the second a point marker is added wherever the points are plotted.

Figure 10-8An example of line plots

This screenshot shows a table of data and three line plots. The data consist of three series organized by row and starting with the words "Widgets", "Gadgets", and "Lumpets". Each of these series has values in five categories. The three graphs illustrate the three sub-types of line plots, with the series plotted independently in the left plot, stacked in the middle plot, and proportionately stacked in the right plot.

Each series in line plots can include three main elements and two error elements, although only the value element is necessary. The series can have a 'Name' element, which is a single text entry used to identify the series, must have a 'Values' element, which is a sequence of numeric values, and may have a 'Label' element, which is a sequence of text entries used to identify the categories. All of these elements can be defined as references to a region of the worksheet, as literally defined entries, or as formula expressions which result in the correct type. The 'Label' element is shared by all of the series. The legend added to a line plot identifies the different series, by default using the entries of the 'Name' element of each series. The two error elements include a list for errors in the positive direction and one for errors in the negative direction.

Table 10-5The data in each line plot series
Element Type Example
Name A single textual entry labeling the data series. These will be used in the legend which may be displayed with the line plot. {"Widgets"}
Value A list of numeric values. {1293, 2502, 3297, 1100, 2487}
Label A list of textual entries labeling each value. Generally, this series will have as many entries as there were in the 'Value' series. These entries are shared by all the series in the line plot. {"North", "South", "Central", "East", "West"}
Error (+) A list of numeric values with as many elements as there were in the 'Value' list. These values can be in the same units as the numeric values in the 'Value' list, can be proportions or can be proportions multiplied by one hundred. {0.10, 0.12, 0.09, 0.11, 0.09}
Error (-) A list of numeric values with as many elements as there were in the 'Value' list. These values can be in the same units as the numeric values in the 'Value' list, can be proportions or can be proportions multiplied by one hundred. {0.08, 0.11, 0.10, 0.09, 0.11}

Line plots provide six icons to choose between three plot sub-types each with two different styles.

Line plot sub-type and style options.

The icon for a line plot of the sub-type with independent, overlapping lines and of the style without point markers.

The icon for a line plot of the sub-type with stacked lines and of the style without point markers.

The icon for a line plot of the sub-type with stacked proportion lines and of the style without point markers.

The icon for a line plot of the sub-type with overlapping lines and of the style with point markers.

The icon for a line plot of the sub-type with stacked lines and of the style with point markers.

The icon for a line plot of the sub-type with stacked proportion lines and of the style without point markers.