The city's unprecedented economic expansion during the past three years has been fueled largely by eye-opening gains in the Bronx, Brooklyn and Queens, as shown by a series of economic snapshots issued by the state comptroller in the past several months. I have compiled the key numbers from those reports together in the accompanying chart.

BRONX BROOKLYN QUEENS Population gain since 1980 26% 26% 19% 25% Percentage of immigrants 37% 36% 47% Gain in businesses since 2007 17% 32% 22% Gain in business sales since 2007 60% 48% 54% Gain in private-sector jobs since 2009 21% 39% 24% Unemployment rate (2017 avg.) 6.2% 4.6% 4.0% Average salary $48,700 $42,500 $48,400 Median household income $37,500 $55,200 $62,200 Poverty rate 28.4% 20.0% 13.6%

The bottom line is similar in all three boroughs: Large population increases fueled by immigration since 1990 have revitalized them and in the past decade have boosted the number of businesses, their sales and the job count. Unemployment also has been reduced to the lowest rate since the government began tracking it in 1990.

It is also possible to distill what is different about the economic progress in each borough.

The Bronx remains the weakest, with the highest unemployment rate and by far the lowest median income. One bright spot is its solid average private-sector wages, better than Brooklyn's and Staten Island's and not much behind those in Queens. Health care is the largest employer in the Bronx, and the big institutions that dominate it pay well. The average Bronx health care salary, $61,100, tops the citywide average for that category.

Brooklyn's story is all about the college graduates flocking to live there. The number of people ages 25 to 34 has jumped by nearly 100,000 since 2000, and the number of residents with a bachelor's degree or higher rose by 15 percentage points to what is now the citywide average, 36%. The borough's average private-sector wage is the lowest in the city, showing a too-heavy reliance on retail jobs.

Queens is the most solidly middle-class of the three boroughs, with a higher average household income and a lower poverty rate than Brooklyn and the Bronx. It is the most diverse borough in the city, and this strength is the result of immigration. The share of its population who are immigrants is higher than any county's in the nation with the exception of Miami-Dade's. The 1.1 million people in Queens born elsewhere is the fourth highest in the country behind Los Angeles County, Miami-Dade and Harris County (Houston).

The comptroller plans a Staten Island snapshot later this year, and when he releases it, I'll update the chart online to include that data.