The economic clustering of cities often ignores the lines drawn on maps.

As Donald Trump continues to insist that Mexico will “reimburse” the U.S. for his wall, his reality-show antics accidentally reveal an important point: What we perceive as authentic borders—like the one between the U.S. and Mexico—can function as artificial constructs, while the imaginary borders that separate rich and poor neighborhoods in the same city can be all too real.

Read the full article at The Atlantic’s CityLab.