The plan specified that most streets would be laid out in a grid. To form the grid, some streets (later named for letters of the alphabet) would travel in an east–west direction, while others (named for numbers) would travel in a north–south direction. Broader diagonal grand avenues, later named after the states of the Union, crossed the north–south-east/west grid. These "grand avenues" intersected with the north–south and east–west streets at circles and rectangular plazas that would later honor notable Americans and provide open space.
Who designed Washington D.C. and what are some interesting attributes about the city?
Washington DC was designed by Major Pierre Charles L'Enfant at the request of George Washington.  L'Enfant was a civil engineer by training, from France, and based his basic design for DC on the streets of Paris.  DC is laid out as a grid, with east-west streets named alphabetically, starting with the letters themselves, and adding syllables as the streets went further out from the city center.  The north-south streets are numbered, increasing as they radiate from the Capitol.  At the intersection of the center-most streets are named for the direction as they radiate from the Capitol, i.e. North Capitol.  However, there is no West Capitol street, as that is the prominent plazas known as the mall.  Diagonally across the grid are streets named after the states and those state streets intersect in circles named after prominent Americans with plazas and open spaces.