In a way, Old Town has had its' own built-in GPS system since the mid-1600's.
House numbering for both "N" & "S" streets begins at King St., with each block being numbered in sequences of 100. For example: the first block off King St. is the 0-100 block; the second block off King is the 100-200 block; etc. So in Old Town, it is always easy to tell: whether you are north or south of King. St.; exactly how many blocks you are off King St.; and whether you are moving either north or south.
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Long & Foster