Wikipedia say a Histogram is a kind of bar graph.
Or more verbosely and more confusingly: A histogram is an accurate graphical representation of the distribution of numerical data. It is an estimate of the probability distribution of a continuous variable (quantitative variable) and was first introduced by Karl Pearson.
The example they give is petal length vs frequency.
I have used it for data that is number of active users in 15 minute buckets
So the x axis is number of users in each discrete 15 min bucket and the y axis is the number of buckets with that number of users, which produced a type of histogram called a Standard Distribution Plot. It had the lower 99.9 percentile as normal and the upper 0.1 percentile highlighted in red as outliers. This was and still is used to work out of monies due for an application with a somewhat obtuse pricing method.
The difference between histogram and bar chart is that bar chart uses the real number of the dimension, where histogram is used to measure the frequency of each number, and histogram separates the numbers into frequency buckets.
I am using right now to measure the moisture of samples out of production. So, let's say I perform 7 tests in a week. I will get numbers like 71%, 71%, 71%, 73%, 76%, 77%, 79%, and so on. I want to know the frequency in buckets of 3. So, the results are.
71-73 = 4
So, instead of using the percentage numbers, the chart uses the frequency (4,1,2). Bar chart does have the logic to build certain chart. It serves to measure frequency of large sets of results for one specific field as measure.
I hope it helps.
For example, I created a table with 20 employees and their ages. I want to know how spread out the ages are, in buckets of 5 years. So, the only dimension I use is Age, and nothing else. I know that the numbers in this dimension are the ages of the employees. Find table below and an image of the histogram. Also I attached the QVF. I hope it helps.
load * inline [
Test Histogram.qvf 176.0 K