Tracking COVID-19 with Gnuplot

Posted on Sat 11 April 2020 in Posts

See this on GitHub with data updates!

I've been wanting to visualize how cases of COVID-19 in New Hampshire are progressing. The State of New Hampshire puts out a daily updates with this information, but it's in narrative form and scattered across PDF files uploaded daily.

So, I decided to use Gnuplot to help me visualize what is happening. I created the text file below with the data from the daily updates, which I gather manually. Each line contains the date in MM/DD/YYYY form, the current number of reported cases and the number of new cases reported. These values are tab-separated.

# covid.dat - COVID-19 statistics in New Hampshire
# Source:

# Date      Cases   Change
3/13/2020   7   0
3/14/2020   7   7
3/15/2020   13  6
3/16/2020   17  4
3/17/2020   26  9
# ...
4/10/2020   885 66

I haven't used Gnuplot much since college, so I had to consult a number of online tutorials to dust off my memory. After a lot of finagling I was able to coax Gnuplot into graphing this data in an attractrive manner.

# covid.plot - gnuplot commands to generate COVID-19 graphs from online data

# Set up output graphic parameters.
set term png
set output "covid.png"

# Set up the graph title, axes labels and graph key.
set title "Number of Persons with COVID-19 in New Hampshire"
set xlabel "Date"
set ylabel "Cases"
set key top left

# Set up the x-axis to show dates.
set xdata time
set format x "%m/%d"

# Tell Gnuplot that we are reading dates in a specific format.
set timefmt "%m/%d/%Y"

# Set up line stylings.
set style line 1 linecolor rgb "red" pointtype 7
set style line 2 linecolor rgb "blue" pointtype 7

# Read data from file and plot into a graph.
plot "covid.dat" using 1:2 with linespoints linestyle 1 title "Total cases", \
     "covid.dat" using 1:3 with linespoints linestyle 2 title "New cases"

This will give me a red line showing the total number of reported cases and a blue line showing the new cases each day. Every evening the State issues its daily report and I manually enter the new data into covid.dat. Finally, I issue the command:

~/src/covid> gnuplot covid.plot

And I get the file covid.png which looks like this: Number of Persons with COVID-19 in New Hampshire