More media outlets are using maps to illustrate the results of the 2018 election. See this story from NPR that uses country level voting to show where the two parties picked up or lost House seats:
Of the 41 congressional districts that Democrats turned from red to blue this election, 38 were suburban, according to an analysis by The New York Times. (Democrats may pick up one to two more seats, once all votes are counted and elections are certified.)
But more granular than congressional districts overall are the counties that compose them. We mapped the percentage of House ballots cast for the party that received the most votes in each suburban county, and we looked at how that compared with 2016.
This map hints at metropolitan regions swinging toward one party or another while still generally adhering to the patterns of big cities and close suburbs vote Democratic and further-flung suburbs vote Republican. Regions like Seattle, San Francisco, Chicago, and Boston swung entirely Democratic. Some were more split: Denver, San Antonio, Miami, Orlando, and Washington, D.C.