Change over time

Line plots are a very useful for comparing sets of data or tracking changes over time. You can plot the data in a 2-D or 3-D view using either a linear or a logarithmic scale.

2D line plot

A 2D line plot uses points connected by line segments from one index to another in the increasing order to demonstrate changes in value. The horizontal axis depicts a continuous progression, often that of time, while the vertical axis reports values for a metric of interest across that progression.

A 2D line plot can be used when you want to emphasize changes in values for one variable (plotted on the vertical axis) for continuous values of a second variable (plotted on the horizontal). This emphasis on patterns of change is displayed by line segments moving consistently from left to right and observing the slopes of the lines moving up or down.

On the horizontal axis, you need a variable that depicts continuous values that have a regular interval of measurement. Very commonly, this variable is a temporal one, generating an observation every minute, hour, day, week, or month. The choice of interval size is a decision that the analyst will usually need to make for the data, rather than it being an inherent data characteristic.

On the vertical axis, you report the value of a second numeric variable for points that fall in each of the intervals defined by the horizontal-axis variable.

Refer to the XY curve section for more information.

Figure 14: 2D line plot

Multiple lines can also be plotted in a single line chart to compare the trend between series. A common use case for this is to observe the breakdown of the data across different subgroups.

Refer to the result set plots section for more information.

Figure 15: Multiple 2D lines plot

Note

If your data are not continuous, another display you can use is the connected dot plot. The Connected dot plot is a way to show how data is distributed or to observe relationships between variables.

Refer to the 2D Line chart and the Connected scatter plot sections for more information.

3D line plot

A 3D line plot uses points connected by line segments from one index to another in increasing order to demonstrate changes in values. Two axes depict continuous progressions while the third axis reports values for a metric of interest across those progressions.

A 3D line plot can be used when you want to emphasize changes in values for one variable for continuous values of two others variables. This emphasis on patterns of change is shown by line segments moving consistently from one point to another in a 3D view and observing the slopes of the lines moving up or down and right or left. This kind of plot is valuable when you want to analyze a trajectory of an object in space.

Refer to the XYZ curve section for more information.

Figure 16: 3D line plot

Logarithmic scale

A logarithmic scale (or log scale) is a way of displaying numerical data over a very wide range of values in a compact way—typically the largest numbers in the data are hundreds or even thousands of times larger than the smallest numbers.

The scale is an axis property. To switch to a log scale, double-click on an axis of the graph and turn on the logarithmic option in the Scale tab of the axis properties window