Stratified graph is not the kind of Bar Plot , Histogram and so on. "Stratify" is one of the process to make graphs.
Left is non-stratified, right is stratified.
Data is same.
This example is Box Plot . But stratified sampling is useful for any types of graphs.
We can compare easily by stratified graphs.
Right type is easier to add data.
There are not many software that can divide graphs by categorical data.
I use ggplot2 in R. And seaborn in Python.
NEXT 
Bar Plot
