HARLEM — Thanks to a Harlem mailman, black families traveling during the Jim Crow era knew where to find hotels, restaurants and auto-body shops willing to welcome their business throughout the country.

From 1936 to 1966, the “Green Book” was a travel guide that provided black motorists with peace of mind while they drove through a country where racial segregation was the norm and sundown towns — where African-Americans had to leave after dark — were not uncommon.

“It’s not just which places are clean and which places serve good food. It’s places that you would be welcomed and you would be safe,” said Maira Liriano, associate chief librarian at the Schomburg Center.

“[Traveling] was hard because you didn’t know which places would welcome you and which places wouldn’t welcome you.”

MORE STORIES: Jimmy Kimmel Parodies Brooklyn Gentrification in 'Do the White Thing'

The Schomburg Center for Research in Black Culture, which is celebrating its 90th anniversary, this year digitized its Green Book collection.

Victor Green, the U.S. Postal Service worker who created the Green Book, published the series from his apartment on Saint Nicholas Avenue in the mid-30s. His wife was from Virginia and he thought it would be a good idea to scout all of the black-friendly businesses along the road to visit her family.

To find them, he tapped into his network of fellow mailmen. The first couple of versions were mostly advertisements from New York, Westchester and New Jersey.

The books were a hit. By the early 1940’s the Green Book included the entire West Coast and much of the Midwest.

Fans of the booklets wrote encouraging letters to Green.

“It is a great pleasure for me to give credit where credit is due,” wrote a fellow traveler Wm. Smith in a fan letter that was included in the 1939 Green Book. “Many of my friends have joined me in admitting that 'The Negro Motorist Green Book' is a credit to the Negro Race. It is a book badly needed among our Race since the advance of the motor age.”

By World War II — during which the Green Book was not published — the annual travel guide included hotels, restaurants, night clubs, taverns and auto body shops from every state and parts of Canada.

In some small towns that didn’t have black-friendly hotels, families listed their own homes as welcome places for travelers. In a way, the Green Book was one of the first forms of couch surfing or AirBnB, librarian Liriano said.

After the war, Green moved into an office and the travel guide became more professional. It had short essays and travel advice from various writers as well as photos of different cities. Green became more vocal in his support for equal rights.

“There will be a day sometime in the near future when this guide will not have to be published,” he wrote in 1948.

“That is when we as a race will have equal opportunities and privileges in the United States. It will be a great day for us to suspend this publication for then we can go wherever we please, and without embarrassment. But until that time comes we shall continue to publish this information for your convenience each year.”

Green continued to publish until he died in 1960, four years before the Civil Rights Act became law.

After he passed, the Green Book continued to be published — some with state-by-state description of new civil rights legislation — until 1966. By then it included parts of Europe, South America and Africa.

The Schomburg’s collection of Green Books has nearly every edition. The only ones it is missing are the inaugural 1936 version and the one from 1952, Liriano said.

Researchers have used them to write books and plays, and one person is in the middle of filming a documentary about the Green Books. Everyone can view them online or at the research library.

“In one little booklet you can get a sense of what it was like to be African-American in that time,” Liriano said.