Invisible Borders - Poland and USA

What are invisible borders?

You can see it on an example from Poland. Poland A and B (Polish: Polska "A" i "B") refers to the historical, political and cultural distinction between the western and the eastern part of the country, with Poland "A", west of the Vistula, being much more developed and having faster growth than Poland "B", east of the river.

This invisible border surprisingly well corresponds with borders of pre-war Poland and Germany.

The western part was much more developed, as You can see on this old railroad map.

Similar situation can be observed also on the USA map:

There are "red" and "blue" states - the elections in many of those are pretty much known before voting takes place.

Before the 2000 presidential election, the traditional color-coding scheme was often "Blue for Republican, Red for Democrat," in line with European associations, where red is used for left-leaning parties, and blue for the right. The colors red and blue also are featured on the U.S. flag. Traditional political mapmakers, at least throughout the 20th century, have used blue to represent the modern-day Republicans, as well as the earlier Federalist Party. This may have been a holdover from the American Civil War, during which the predominantly Republican north was considered "blue". However, at that time, a maker of widely-sold maps accompanied them with blue pencils in order to mark Confederate force movements, while red was for the union.

What are other examples of Invisible Borders? Please share in comments!