Why is the article the map that shows that the city vs. country is not our political fault line a secondary source?

Explanation:

FREEPORT, Maine — Contrary to conventional wisdom, the most significant and abiding divide in American politics isn’t between city and countryside, but rather among regional cultures. Rural and urban places certainly have distinct interests and priorities, but in our awkward federation their differences have taken a back seat to the broader struggle between our constituent regions.

Sectionalism isn’t, and never has been, as simple as North versus South or an effete and domineering East against a rugged, freedom-minded West. Rather, our true regional fissures can be traced back to the contrasting ideals of the distinct European colonial cultures that first took root on the eastern and southern rims of what is now the United States, and then spread across much of the continent in mutually exclusive settlement bands, laying down the institutions, symbols and cultural norms later arrivals would encounter and, by and large, assimilate into.

Understanding this is essential to comprehending our political reality or developing strategies to change it — especially as we approach a momentously consequential midterm election.

use wikipedia, i think they have this.