Google N-gram viewer: compare frequency of terms found in books

[kurumi]

It's probably easiest to start with an example:

http://books.google.com/ngrams/graph?content=freeway%2Cexpressway%2Cmotorway&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=

This is a chart of how many times the terms "freeway", "expressway" and "motorway" are found in Google Books over the years.

You see nothing until about 1932, when freeway and expressway rise together for a few decades. At 1960, "freeway" keeps rising and "expressway" falls off; in 1975 "motorway" catches up and surpasses "expressway".

You can also check phrases, as in this 5-way battle between interstates 10, 40, 70, 80 and 90: http://books.google.com/ngrams/graph?content=Interstate+10%2CInterstate+40%2CInterstate+70%2CInterstate+80%2CInterstate+90&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=

(Interstate 5 beats them all.)

[on_wisconsin]

Like this:
http://goo.gl/2d6Yo