Why is india called the world's largest democracy

Its all about population India has 1.26 billion people where as second largest US has 315 million.

Also India has a 3 tier administrative system.

All levels have elections.

One of the most costliest elections as the government spent millions in conducting it through a independent body.

The election is 2nd most expensive election in terms of money spent by the candidates. As first place is US presidential election.

where is the picture? ?