Manufacturing jobs disappeared: This story we knew already. Machine operators and factory workers had a dominant presence in the Midwest and parts of the South through the late ’70s. Then a combination of globalization and technological change made many of those jobs disappear.
Fewer and fewer farmers: Our map shows the tail end of a century-long trend. Farming technology (everything from tiny seeds to giant harvesters) keeps getting better, which means fewer and fewer people can grow more and more food.
Government: The most common job in D.C. is lawyer. Heh. On a related note, Northern Virginia is full of federal contractors — many of whom work as software developers.