According to Bob Arnebeck, author of Through A Fiery Trial:  Building Washington, 1790-1800, the real answers are prosaic. There’s no J Street because, back then, typography had yet to be standardized, and I and J were often used interchangeably. Of course, notes Arnebeck, so were U and V. But, he suspects, those letters made the cut because L’Enfant was trying to get to the edge of his map without having to use “X,” a letter that in those days was often used to signify Christ. As for Y and Z, Arnebeck says, “I think they simply ran out of streets.” The original boundary of the city was what is now Florida Avenue, which rises just a block north of V.