What is a Line Chart?


Line charts are ideal for showing trends over time. A standard example would be how the stock value for a certain company develops over time on the stock market. However, it does not necessarily need to be time along the X-axis, any data that behaves like a function with respect to the variable on the X-axis can be plotted. Line charts emphasize time flow and rate of change rather than the amount of change. Multiple scales can be used on the Y-axis to when you want to compare several lines with significantly different value ranges.

 

You can select parts of a line by clicking and dragging with the mouse. If one node in the line is included when you drag, that node will be marked. If two or more adjacent nodes are included, the line between the nodes will also be marked, but if there are nodes in between which aren't included, only the separate nodes will be marked. You can select several nodes in different parts of the line by pressing Ctrl and click and drag with the mouse. By pressing Alt, the entire line is marked if you click and drag, just as it is if you simply click once anywhere on the line.

 

If applied when the analysis was created, the line chart can display additional information in reference lines or several different types of curves. These lines or curves could, for example, show how well your data points adapt to a certain polynomial curve fit, or to summarize a collection of sample data points by fitting them to a model that will describe the data and display a curve or a straight line on top of the visualization. The curve usually changes appearance depending on which values you have filtered out in the analysis. On mouseover, a tooltip shows how the curve is calculated.

Example:

Below is a line chart showing the sum of sales for two different product categories over several years. The line chart has one color (one line) per product category.

line_chart_web.png

Error Bars

Error bars are used to indicate the estimated error in a measurement. In other words, an error bar indicates the uncertainty in a value. Used in a line chart, error bars look like this:

vis_error_bars3.png