There are sister states like Georgia and Alabama, and Mississippi and Louisiana. New Jersey and California, on the other hand, split in half because of the influences of large cities. Chattanooga, Tenn., communicates more with the Georgia-Alabama community than with the rest of Tennessee, and Pittsburgh splits from Pennsylvania to align with West Virginia. Texas remains whole, because the communication among Dallas, Houston, San Antonio and Austin is strong enough to hold it together.
These patterns show that proximity is only one of many factors — both cultural and economic — that bring people together.