The semantics aren't exactly meant to be "% of land area", but they do represent a rough coordinate system[1], from (5, 8) in the SW corner of the contiguous US

The semantics aren't exactly meant to be "% of land area", but they do represent a rough coordinate system[1], from (5, 8) in the SW corner of the contiguous US (San Diego) up to (95, 90) in Boston. Interestingly, US highways follow the opposite system[2], going from (1, 2) in the NE corner of the country (Maine) to (former) (101, 80) in San Diego. [1] https://en.wikipedia.org/wiki/Interstate_Highway_System#Numbering_system https://en.wikipedia.org/wiki/Interstate_Highway_System#Numb... [2] https://en.wikipedia.org/wiki/United_States_Numbered_Highway_System#Numbering https://en.wikipedia.org/wiki/United_States_Numbered_Highway...