Each coloured shape in the graph represents a platform. Horizontal axis is time. The vertical axis represents the number of games released. So the height of a shape on a given point in time indicates the number of games released for that platform that year. The total height of the graph on a given point in time shows the total releases that year.
All data taken from MobyGames. Of course the graph is only as complete as our database is.
Some interesting tidbits:
In the 2009 graph the peak in the late 80s was higher than the late 00s peak. In the 2010 graph they were roughly equal in height. Now the latter peak is in a whole different league. Can we get it double the size next year?
Probably the best populated newly added (this year) platform is Windows Apps, barely visible as an orange smudge below the Wii U.
There are actually quite some PS4 and XBone games, but the verticality in that part of the graph makes it look worse than it is. The Game Boy (noted as GB on the graph) and FM Towns suffer a similar faith.
Our number of "last year" titles is historically quite low over all the years. Last year's graph was excellent with 2915 titles of 2014 present. This year is not so bad either with 2583 titles of 2015 present.