Histogram

What is a histogram?

A histogram is a set of rectangles (bars or columns) that shows a distribution of numerical variables over a scale divided into bins. Each rectangle represents the accumulated value (a range) of the given bin.

A histogram is a type of chart that resembles a bar or a column chart. But for the visual distinction between a histogram and a bar chart, it’s customary not to leave gaps (or to make them very small) between rectangles in a histogram to show the continuous nature of the variables used in the visualization. the columns have different heights because they correspond to the frequency of each group - meaning, how many items fall in a certain range.

Histograms are quite often chosen as the first option to review the data. They allow us to quickly see the form of distribution.

Bin sizing

The size of the bin is the ultimate customizable option for a histogram, depending on the size of the bin the form of the histogram can be changed drastically. It’s better to follow your data’s logic, but there’s also a popular way for choosing a bin size called Sturge’s rule. It’s used in all major software, but it was criticized for over-smoothing histograms.

The formula is the following: K=1+3.322 log(n),

where:
K is the number of bins
n is the number of observations in a dataset.

Labeling

In most cases, the histogram is used to see the form of distribution and overall pattern, so there’s no need for detailed labeling of every bar. A regular axis label for both axes should work.

Coloring

Coloring of histograms follows the general rule of using color in data visualization – use color only if it communicates additional information. For any basic histogram, one color should be enough.

Highlighting

To draw attention to the most important bin(s) of a histogram, a good solution is to highlight these bin bars and color all the others – in a neutral color. Our brain is programmed to notice deviations instantly. This can be done, for example, by applying changes in size, movement, or color. This way, highlighting a specific bin will help catch the reader’s eye immediately.