XY Chart

Overview

An XY chart visualizes relationships between numerical data and allows you to find correlations in the data. Data can be presented as a scatter plot or a bubble chart.

XY Scatter Plot

A Scatter Plot is an XY chart in which we draw data points based on two numeric values. One value determines the horizontal (X) position, and the other value determines the vertical (Y) position. We study the relationship between these two values to see if one value could predict the other because they are correlated.

A trend line can assist in seeing such a relationship.

• linear - a linear trend line is a straight line that passes as close as possible to all points (it minimizes the distance from all points). This is called a linear regression line. If the points appear to be close to the trend line, then the two values would appear to be correlated.
• LOESS - this line minimizes distance from points in its vicinity. The smooth line is not straight but rather follows the points as close as possible. This is similar to a moving-average line in a stock chart, however an LOESS calculates a weighted average in which points that are closer to the line get a higher weight than outliers (points that are distant from the rest of the data). An LOESS line can show non-linear relationships.

Bubble Chart

In a bubble chart we show a third numerical value. We represent this third value by varying the size of each point which we now call a bubble. We make the area of the bubble proportional to the value and therefore larger bubbles represent a larger value for this third value.

Tooltop

A "Tooltip" is the yellow rectangle that looks like a sticky note and appears next to a point in the graph to provide detail. To see the tooltip you hover the mouse over the point. On a touch device, simply touch the point for which you'd like to see the tooltip.

Zoom

You can easily zoom on an area of the chart by selecting a rectangle in the chart viewing area. To make the selection point the mouse at the beginning of the selection and then click the mouse and drag it diagonally while clicked to select a rectangle. When you release the mouse button the selection is complete. On a touch device, you begin the selection by touching with your finger and then you drag your finger diagonally to draw a rectangle. When you lift your finger off the screen, the selection is made. You can zoom in repeatedly to focus on smaller areas of the chart. Finally to zoom out click the Reset Zoom button.