So that is a graph of average house prices divided by the median salary (average but not allowing extreme salaries to distort the value), or in other words how many average salaries you would need to buy a house. The figures were originally obtained from UK government statistics.
The graph is a little small, but it shows that in 1977, the multiple was roughly 0.9 increasing to nearly 7 by 2019.
Now there’s all sorts of factors involved but fundamentally that is a huge increase in housing costs as proportion of our salaries.