Dar al-Hijra is on Leesburg Pike. Less than 1 1/2 miles east, straight down Leesburg Pike, is the Skyline apartment/condominium complex, a series of 8 or 10 highrise apartment buildings that have a huge number of Muslim/Arabic/North African occupants.
It's worth noting that immediately after 9/11, the FBI was making repeated visits to various Skyline buildings, and that significant number of occupants either disappeared or left the country under federal suprvision.
At the southeast corner of the Skyline complex (at Seminary and South George Mason) is a strip shopping mall called "Plaza America" which ironically is also called "Little Arabia" or something like that due to the overwhelming number of Middle Eastern shops, restaurants, and coffee houses.
There is another smaller strip mall of Middle Eastern shops about halfway between Dar al-Hijra and Skyline, and also on Leesburg Pike. That mall is almost directly across Leesburg Pike from the 5913 Leesburg Pike apartment address used by many of the 9/11 hijackers on their phoney Virginia ID cards.
Finally, many of the Muslim "social" organizations (e.g., Muslim Youth Association, World Assembly of Muslim Youth, American Muslim Association) either now or in the past have run their operations out of this little section of Northern VA, most of the time using PO Boxes from the Bailey's Crossroads post office (zip code 2204x). Many of the leaders of these groups live in the Skyline complex.
Stephen Schwartz (see "Wahhabis in the Old Dominion") has done a lot of other research on the activity around Dar al-Hijra, including its leadership and the clear ties to the financial groups raided last year in Herndon. Also there are fairly clear links to the bin Laden family and Dar al-Hijra, though I believe most of those have been identified and probably shut down or reduced.