Thus the boundaries of the Downtown district, subtracting the above-mentioned neighborhoods, are somewhat irregular and difficult to define. The core of the area lies roughly between Constitution Avenue to the south, M Street to the north, 17th Street to the west, and 12th Street to the east. North of Pennsylvania Avenue NW, and extending five additional blocks west of 17th Street to 22nd, is also considered "downtown." On the east, and south of Pennsylvania, another section of the business district stretches seven blocks to the intersection of Pennsylvania and Constitution, forming a triangular group of government buildings known as the "Federal Triangle". [1]