प्राचीन दक्षिण भारतीय इतिहास में 'संगम' शब्द का तात्पर्य निम्नलिखित में से किससे है?

In Ancient Indian Statecraft, Kautilya's 'Rajamandala' theory primarily deals with:

The First Buddhist Council was held at ______.

Which ancient Indian text contains references indicating that population counts or census-like records were maintained in ancient India?