Drawing the system…
The 48,471 miles of the Eisenhower System, drawn as the only ink on the sheet and tinted by the National Weather Service forecast on the pavement: temperature, sky, wind, rain and snow, seven days out. 2,187 miles are under an NWS alert right now.
There is no basemap under this. No terrain, no counties, no coastline — the only ink on the sheet is 48,471 miles of Interstate, and the country appears anyway, because the system was built to describe it. That is the whole idea borrowed from the 1957 Yellow Book, the slim federal volume titled General Location of National System of Interstate Highways that showed the thing as pure linework before a yard of it was poured.
Every road is tinted by the weather on it. Values come from the National Weather Service's NDFD grid at 2.5 km, sampled at 5,580 points spaced about eight miles apart along the pavement, then blended between those points so a front crossing a route moves down it smoothly instead of stepping from marker to marker. Nothing here is interpolated from city observations: it is the gridded forecast, read where the road actually is.
The temperature scale is diverging about 32 °F rather than running a rainbow from cold to hot, because on a road the freezing point is not one value among many — it is the value. Sub-freezing pavement is also drawn heavier, so the hazard is carried by a second channel and never by colour alone.
And the numbers rise as you go north. I-10 hugs the Gulf; I-90 runs the northern tier from Seattle to Boston. Two routes ending in 0 are the long transcontinentals.
And the numbers rise as you go east. I-5 is the Pacific coast, I-95 the Atlantic. The rule is the exact inverse of the US Highway system it replaced, which is why the two never collide on a sign.
The last two digits name the parent. An even first digit is a loop that returns to it — I-495 around Washington. An odd first digit is a spur that does not. Six numbers are worn by two unconnected roads each; the map keeps them apart.