How Long Is the Mississippi River?

By on May 20, 2013 in education, Playtime | 6 comments

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How Long Is the Mississippi River?

Scatter plot.

As long as my grandson has been willing to play around with graphs recently, we have been trying to come up with more things to graph.

English: A scatter plot with trend line of bab...
A scatter plot with trend line of baby age to height. (Photo credit: Wikipedia)

After we graphed the number of letters in state names and the size of states in area and population, we turned to rivers and created scatter plots.

One of the things I found out in all this graphing activity is that you have to figure out how many lines you have available on your graph paper, in both directions, across the top and up the side. Then, find out the highest numbers you will need. That way, you can figure out what numbers to put on the left side, or vertical or y-axis, of your graph, or across the bottom, the horizontal or x-axis.

For example, what is the longest river in the United States? If you had said the Missouri, you’d be right (2,341 miles). If you’d said the Mississippi, you’d be close (2,202 miles). It is the second longest river. Then, come the Yukon (1,979 miles) and the Rio Grande rivers (1,759 miles).

Let’s get graphing!



Why Is This Useful?

One of the first things you will notice when you have all 15 dots on your U.S. river graph, or all 20 on your world river graph, is that the dots tend to cluster. Seven of the U.S. rivers lie between the 800-mile and 1,200-mile lengths. No other 400-mile range has so many rivers. Similarly, six of the longest rivers in the world lie in the 3,200-mile to 3,800-mile range and six lie in the 4,200 to 4,700-mile range.

Scatter plots make it easy to see patterns like this.

One of the best examples comes from statistician Edward Tufte,  who specializes in making information easy to understand with graphs. One of his most dramatic examples is a scatter plot showing how much more often a critical component of a rocket ship, the O-ring, failed as the temperature dropped.

He argues that had the information been displayed in a scatter plot instead of the timeline that was used, it would have been easy for engineers and managers to see how unsafe it was to allow the Challenger to launch when the temperature was below freezing, and avert what came to be the Challenger disaster. Instead, they were left with the fact that sometimes an O-ring didn’t fail at temperatures below freezing, instead of seeing that the cluster of successful launches were well above freezing and very few successful launches were below freezing.

On January 28, 1986, the Space Shuttle Challenger was given permission to launch, broke up 73 seconds into its flight and seven astronauts died.

For lack of a scatter plot.


Carol Covin, Granny-Guru

Author, “Who Gets to Name Grandma? The Wisdom of Mothers and Grandmothers”

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