In Tuesday’s election, House districts on the outskirts of major American cities were the site of electoral shifts that propelled Democrats to power.

Wealthy and middle class voters delivered the suburban votes for enough Democratic pickups to secure a majority. In several cases, the battleground districts were wealthy and highly educated places that Hillary Clinton won in 2016, exposing the vulnerability of those Republican lawmakers.

The addition of quality mapping data in recent years to stories about election results is great. It helps highlight the clear patterns from recent elections regarding where the two parties have stronger bases, Democrats in cities and close suburbs and Republicans in rural areas and further suburbs.