This map shows the insane growth of million-dollar homes in New York City

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Brooklyn, one of New York City's five boroughs, has seen an explosion in million-dollar homes over the past four years.

In some US cities, million-dollar homes are becoming the norm.

Take San Francisco, where 57% of homes have a value of $1 million or more - or San Jose, where 46% are seven-figure homes.

That's according to real-estate site Trulia, which looked at the share of million-dollar homes in the 100 largest US metro areas and how it's grown over the past four years. It defined a million-dollar home as any home - regardless of whether it's listed for sale - with a value of $1 million or more.

While New York City has a small share of seven-figure homes compared to San Francisco and San Jose - it moved from 7% in May 2012 to 12% in May 2016 - certain neighborhoods, particularly in Brooklyn, have seen an explosion in million-dollar homes over the past four years.

Bedford Stuyvesant, a neighborhood in the north central part of Brooklyn, moved from 1.7% of homes valued at $1 million or more in 2012 to 56.5% in 2016. That's more than a 3,000% increase. Another Brooklyn neighborhood, Greenpoint, saw an increase from 8.4% in 2012 to 56.7% in 2016.

You can get a better idea of the insane growth of million-dollar homes in the New York metro area over the past four years by looking at this heat map:

Trulia