Question: Which city is the metropolitan area that contains the Independent School League centered on?

Context paragraphs:
Ethical Culture Fieldston School: Ethical Culture Fieldston School (ECFS), known as just Fieldston, is a private, highly selective independent school in New York City.  The school is a member of the Ivy Preparatory School League.  The school serves approximately 1700 students and 325 faculty and staff.  Jessica L. Bagby has been the Head of School since June 2016.  The school consists of four divisions: Ethical Culture, Fieldston Lower, Fieldston Middle, and Fieldston Upper.  Kyle Wilkie-Glass is the Chief Operating Officer, Jodi Scheurenbrand is the Chief Financial Officer.  Ethical Culture, located on the Upper West Side of Manhattan, and Fieldston Lower, located on the Fieldston campus in the Riverdale section of the Bronx, serve Pre-K through 5th Grade.  The two lower schools feed into Fieldston Middle (grades 6–8) and Fieldston Upper (grades 9–12)—also located on the Fieldston campus in Riverdale.  Ethical Culture is headed by Rob Cousins, Fieldston Lower is headed by Noni Thomas Lopez (Interim Principal), Fieldston Middle is headed by Chia-Chee Chiu (New Principal), and Fieldston Upper is headed by Robert J. Cairo (Interim Principal).  Tuition and fees for ECFS were $48,645 for the 2017-18 school year.

Latin School of Chicago: Latin School of Chicago is a selective private elementary, middle, and high school located in the Gold Coast neighborhood on the Near North side of Chicago, Illinois, United States.  The school was founded in 1888 by Mabel Slade Vickery and is the oldest independent day school in Chicago.  The school is a member of the Independent School League

La Marque High School: La Marque High School is a public high school in La Marque, Texas, United States in the Houston Metropolitan Area.  The school, which serves grades 9 through 12, is currently a part of the Texas City Independent School District; prior to July 1, 2016, the school district was a part of the La Marque Independent School District.  After TCISD annexed LMISD, the school remained open, and its athletic teams continued to be separate from those of Texas City High School.

Washington metropolitan area: The Washington metropolitan area is the metropolitan area centered on Washington, D.C., the capital of the United States.  The area includes all of the federal district and parts of the U.S. states of Maryland and Virginia, along with a small portion of West Virginia.

Independent School League (Washington, D.C. area): The Independent School League or ISL is a group of seventeen preparatory schools located in the Washington metropolitan area of the United States that compete with each other athletically.  All competitors in the ISL are girls, but not all schools are "all-girls" schools.  The league is broken into two divisions: A and AA.  The schools which compete in each division vary by sport.

Belmont Hill School: Belmont Hill School is an independent boys school on a 32 acre campus in Belmont, a suburb of Boston, Massachusetts.  The school enrolls approximately 440 students in grades 7-12, separated into the Middle School (grades 7-9) and the Upper School (grades 10-12), and refers to these grades as "Forms" with a Roman Numeral I through VI.  While the majority of attending students are day students, there are some who enroll in the school's five-day boarding program, which becomes an option for students in their 9th grade year.  In addition to the school's history of academic prestige, the school exhibits a rich athletic tradition as a participant in the competitive Independent School League.  Members of the Class of 2010 were accepted at 42 colleges and universities.  Belmont Hill is also a founding member of the International Boys' Schools Coalition.

Forest Lake Area High School: Forest Lake Area High School, also known as Forest Lake High School, is a public three-year high school in Forest Lake, Minnesota founded in 1909.  The school is a member of Minnesota Independent School District 831 (Forest Lake Area School District).  The school competes in the Suburban East Conference of the Minnesota State High School League

Mid-Atlantic Athletic Conference: The Mid-Atlantic Athletic Conference (MAC) is an American high school athletic league composed of private schools in the Washington, D.C. area.  The conference was founded in 1994.  Solely male teams participate in the conference.  As every member school is co-ed, the girls compete in the Independent School League, or ISL.  The MAC is often considered as competitive as the IAC and the WCAC, and more competitive than the PVAC, the three other Washington-area private high school conferences.  While the MAC generally boast fewer students than schools in the WCAC they tend to be just as competitive in sports.  For example, Saint James has a total student body population of 235, a number which comprises both boys and girls.  Gonzaga College High School, meanwhile, an all-boys school in the WCAC, has an enrollment of roughly 900.

Middlesex School: Middlesex School is a coeducational, non-sectarian, day and boarding independent secondary school for grades 9-12 located in Concord, Massachusetts.  It was founded as an all-boys school in 1901 by a Roxbury Latin School alumnus, Frederick Winsor, who headed the school until 1937.  Middlesex began admitting girls in 1974.  The school is a member of the prestigious Independent School League and is one of five schools collectively known as St. Grottlesex.

Saint Sebastian's School: Saint Sebastian's School is an independent, all-boys Catholic secondary school located in Needham, Massachusetts on 26 acre .  The school instructs young men in grades seven through twelve.  Founded in 1941 by William Cardinal O'Connell, Archbishop of Boston, the school is named after Saint Sebastian, the Christian martyr who survived an attempted execution by arrows.  It is the only Catholic school in the Independent School League.  Approximately 350 students are enrolled, with 25% receiving financial aid.  Since 1990, the School headmaster is Mr. William L. Burke III.

Supporting paragraphs: Independent School League (Washington, D.C. area) Washington metropolitan area
Answer: Washington, D.C.