The religious face of the United States is largely Christian, with roughly seven-in-ten Americans belonging to that faith, but some of the biggest U.S. metropolitan areas have a very different look, a Pew study shows.

Only about half of the residents in the Seattle (52 per cent) and San Francisco (48 per cent) metropolitan areas identify as Christians, as well as roughly six-in-ten or fewer of those living in Boston (57 per cent) and New York (59 per cent).

The Pew Research Center's 2014 Religious Landscape Study released July 30 was designed to look at the religious affiliations of Americans overall as well as those in all 50 U.S. states and the 17 largest metropolitan areas.

While Christians make up between 65 per cent and 75 per cent of adults in most of those metro areas - and people with no religious affiliation generally make up roughly 20-25 per cent of the population - some cities stand out for a variety of reasons.

The study found that Boston, Seattle and San Francisco have relatively few Christians

Seattle, San Francisco and Boston are also notable for their considerable populations of religious "nones" (atheists, agnostics and those who say their religion is "nothing in particular").

A third or more of people in each of those metropolitan areas (37 per cent in Seattle, 35 per cent in San Francisco and 33 per cent in Boston) are religious "nones."

One-in-ten Seattleites are self-identified atheists (10 per cent), while 6 per cent are agnostics. In San Franciscans 10 per cent call themselves agnostics, compared with 5 per cent who are atheists.

Nearly a quarter of New Yorkers are religiously unaffiliated (24 per cent), but the city also is home to relatively high numbers of members of non-Christian faiths.

Nearly one-in-ten New Yorkers (8 per cent) are Jewish, 3 per cent are Muslim and another 3 per cent are Hindu.

JEWISH SHARE

Among the 17 largest metropolitan areas, New York's Jewish share is matched only by Miami (9 per cent).

Moving south, roughly three-quarters of residents of three cities - Dallas (78 per cent), Atlanta (76 per cent) and Houston (73 per cent) - are Christians.

In each case, at least three-in-ten are evangelical Protestants (including 38 per cent in Dallas).

And Atlanta, the birthplace of Martin Luther King Jr. is home to an especially large share of members of the historically black Protestant tradition (18 per cent).

Three of the most heavily Catholic cities also are the nation's three largest cities. About a third of residents of New York (33 per cent), Los Angeles (32 per cent) and Chicago (34 per cent) are Catholic.

In each of these cities, fewer than one-in-five residents are evangelical Protestants (including just 9 per cent in New York) - compared with a quarter of U.S. adults overall who are evangelicals.

Among the nation's biggest metro areas, Phoenix has one of the highest concentrations of Mormons (6 per cent). But this analysis does not include smaller cities, such as Salt Lake City, that may have a larger proportion of Mormons.