But what is the right way to number houses? Enter the Philadelphia system: odd numbers on one side of a street, even numbers on the other. An adviser to George Washington, Clement Biddle, devised this system in 1790 when Philadelphia was conducting a census. Odds on one side, evens on the other takes much of the guesswork out of knowing how far a number is along a street. In Philadelphia, this system was revised in the nineteenth century to make house numbering even more logical, assigning one hundred numbers to each block, with the numbers shifting to the next hundred at the next block.
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