The usual axis along which Indian states are divided is horizontal—the relatively advanced southern states versus the relatively backward states north of the Vindhyas.
Prime Minister Narendra Modi mentioned a different grouping based on a vertical division this week.
He said eastern India is lagging behind western India. He specifically mentioned eastern Uttar Pradesh, Bihar, Assam, Odisha and West Bengal.
Part of this is undoubtedly the usual claims of partisan politics. The Bharatiya Janata Party (BJP) is weaker in the eastern parts of the country.
However, there is also an element of truth in what Modi said. Even western states such as Rajasthan that were once considered laggards have made impressive progress.
What is even more puzzling is that some of the eastern states have not been able to build diversified economies, despite the fact that they face the most dynamic parts of the global economy, stretching from Thailand to China.
Why this is so needs to be understood better.