Log Graphs
On log scales, multiples of each number have even spaces.
COVID-19 reporting may involve graphs showing cases and deaths. Data journalists often show these figures with logarithmic scales.
This article discusses logarithms, scales, and how to interpret these graphs.
What is a logarithm?
One Financial Times graph shows a rolling average of daily deaths on a log scale. John Burn-Murdoch created this graph:
Addition and multiplication are two fundamental operations in arithmetic. There is a third: exponentiation. For whole numbers, this is where we multiply a number over and over again.
For example, 10 times 10 times 10 is 1,000. A short way of writing that repeated multiplication is: 10³. An alternate way of saying this is ‘10 raised to the power of three’.
Each of these three operations has inverses: operations that undo. Subtraction is the inverse of addition. Division is the inverse of multiplication. Logarithms are the inverse of exponentiation.
Using 10 as our base, the logarithm of 1,000 is 3. This is because 10³ is equal to 1,000.
Log scales
On a standard linear scale, 10 would be the same distance from 20 as 20 is from 30. There…
