Spain has a lot to lose if Catalan secessionists are successful in their breakaway plan.

Catalonia makes up only 6 percent of the country’s territory and 16 percent of its population, but it accounts for a fifth of economic output, a quarter of exports, over half of new startup investment in 2016 — and nearly a third of Spain's Rio Olympic medalists.

Independence supporters will gather Monday in Barcelona to celebrate the Catalan national day, ahead of the October 1 referendum on secession called by the regional government in defiance of Madrid and the Constitutional Court. Spanish Prime Minister Mariano Rajoy's government has pledged to do everything in its power to stop the vote from happening.

While a majority of Catalans don't see independence as the ideal way forward, Madrid’s unwillingness to negotiate could still result in a secessionist victory in the knife-edge referendum.

Here's how national sentiment, language, place of birth and more play a part in determining support for independence, and what Spain could wave goodbye to if Catalonia does break away.

CORRECTION: An earlier version of this article had some incorrect text references to the data in graphics.