…If you picked row two; number four, go get yourself a Faygo Grape Slurpee! You earned it.

See, the eight clear lines on Detroit’s histogram represent two separate grids. There’s one aligned on an East-West, North-South axis — think 8 Mile and Wyoming — and another one that’s off-kilter, that uses the angle of the Detroit River shoreline as its guide — aka, Mack and John R.

Courtesy Geoff Boeing. Click for labels.

Detroit isn’t unique for having two separate grids — you see two grids in San Francisco and St. Louis, among others — but “it is unusual in how clear they are,” Boeing told Detour in an email. “There is little else to obscure them in the histogram, and they are substantially offset so they stand apart from each other.”

The shoreline grid developed first, following the paths of the 18th century ribbon farms shooting perpendicular off the river. In the city’s northern and western areas, you’ll find the streets, built later, that were designed to follow the cardinal directions.

These two different grids can lead to abrupt breaks in the flow of the city, explains “Detroit’s Patterns of Growth,” a 1965 short film from Wayne State University.

“Many of Detroit’s traffic problems are located at points where the grid and shoreline systems come together,” the narrator says. He name checks the Davison, which runs straight west from Van Dyke, then swerves south to follow the river, then at Livernois jogs back to head west for a few blocks before sputtering out. Over the course of its supposedly crosstown route, the thoroughfare starts north of McNichols, or 6 Mile, and ends up a block south of Schoolcraft, or 4 Mile.

On the west side, the grid system often switches at Livernois Avenue.

The two grids aren’t the only street systems affecting the organization of the city’s streets — Boeing’s rendering, mapping street frequency, doesn’t account for the radial spokes of Fort, Michigan, Grand River, Woodward, Gratiot and Jefferson, built along Native American trading paths. Nor does it reveal the small fragment of Augustus Woodward’s Plan of Detroit that got built in the 1800s at the heart of downtown — these two other organizational patterns intersect the other grids and are an outsize influence on how we visualize and navigate the city. And don’t even get us started on how the freeways sliced up the map.

We’ll leave you with the opening lines of that prescient planning video: “To an overhead observer, the street pattern of Detroit presents a strange mosaic of conflicting systems, which seem to start and end with no apparent reason and have no relation to each other. However, the twists and turns have their historic explanations.”

Whether they make sense from the ground is another story.