Last week the Texas Tribune posted maps of last Tuesday's primary runoff results by county for both the Republican and Democratic US Senate runoffs. In the Democratic runoff, Sadler won a majority in nearly 90% of counties holding elections, but earned only 63% of the vote against Yarbrough. To get a sense of where the 37% of Democrats who voted for Yarbrough were disbursed I've used the Tribune's data to create a new map expressing Yarbrough's percent of the vote. Heavier purple indicates more support.
There's a clear Yarbrough bump running diagonally across South and West Texas. Sadler soaked up votes from Central Texas and the Hill Country. The urban areas don't stand out in any sense really other than Travis County which voted for Sadler at the highest rate of Texas' most populous counties.