5 Steps to Create a Measles Chart

Measles Chart Basics

The clever Dr. John Snow mapped cholera cases during the epidemic of 1854 on a street map of the area. This type of mapping now called a measles chart, or defect location check sheet, or defect map, is useful when exploring the effect of location data.

The name measles chart may have come from the habit of using an image of drawing of a product and adding small red dots to signify defect locations.

Benefits of Measles Charts

There are different types of data including continuous, attribute, and location. While it is often a best practice to use continuous data whenever possible, converting locations data to continuous may lose useful information.

The benefit is we can map the location on a two-dimensional image or drawing, or we can (if clever) plot in three dimensions. The idea is to look for clusters patterns, much as Dr Snow is in the mid-1800’s/

Plotting the location of failed bearings along a conveyer belt system may reveal areas with a misalignment thus increase load or stress on the bearings. Plotting the location of solder joint defects or failed components may reveal an unwanted heat flow across the circuit board.