RQ | Rail length growth in India, or why you should not trust visualizations at face value

My colleague Nitin Pai extracted some data from the latest issue of EPW that shows the growth in total route length of Indian railways in the last 20 years. To get a better understanding of how the rail length has grown, I draw a simple graph. This is what I found:

Data source: Economic and Political Weekly May 18, 2013 vol xlviII no 20

Data source: Economic and Political Weekly May 18, 2013 vol xlviII no 20

From this graph, it looks like the growth in Indian Railways route length has been pretty impressive. You will also notice that the graph is not monotonically increasing – there are years where the route length is lower than that of the previous years. I would suspect that is due to conversion of metre gauge to broad gauge tracks.

But then if you take a closer look at the graph, you might notice that the y axis doesn’t start at zero. So you might want to see what the growth looks like if you were to start the y axis at zero. Here is what you get:

Data source: Economic and Political Weekly May 18, 2013 vol xlviII no 20

Data source: Economic and Political Weekly May 18, 2013 vol xlviII no 20

Now that the axis has been plotted starting from zero, you notice that the growth in rail length by the Indian railways is not all that impressive.

Moral of the story: If you are a user of a visualization, make sure you check things like axes, scales, etc. before jumping to conclusions. You never know what tricks the person who made the visualization might have been up to. If you are making a visualization, however, keep in mind that a lot of your consumers are not going to look at the visualization too carefully, so make use of axes, scales, etc. in a way that embellishes your story.