New Delhi, July 8 -- Prime Minister Narendra Modi's call for district-level GDP estimates, made at the 11th Niti Aayog Governing Council meeting, was welcome. For too long, Indian economic policymaking has been driven by aggregates that obscure as much as they reveal.

But before enthusiasm outpaces architecture, one question must be settled: who produces these numbers, how and whose numbers count? The answer matters enormously. Getting it wrong could produce a statistical exercise that is politically convenient but economically hollow.

There are, broadly, two approaches to estimating district domestic product (DDP).

The first, and currently dominant, is top-down: start with the national or state GDP and allocate shares downward using p...