Wednesday, February 1, 2017

Why the North-South Chicago Streets Don't Line up at North Avenue.

Chicagoans know that the north-south streets swerve abruptly on crossing North Avenue (1600 north) from Kedzie Avenue (3200 west) to Oak Park Avenue (6800 west), a distance of four and one half miles.
Crawford Avenue (Pulaski) looking north towards North Avenue, Chicago - 1947
THE MYTH
Chicago’s streets are a grid pattern which is then overlaid on a spherical map of the Earth. All grids overlaid on spheres create an issue. As the meridians lines (north/south) approach the poles, they converge.

A surveyor laying out a grid has two choices. Either let the streets get closer together as they head towards the North Pole, meaning the building lots get smaller and thus can be sold for less, or readjust the grid at intervals so that the lots, and thus the profits, don't shrink.

Chicago opted for the second choice. The abrupt readjustment, or so the story has it, is manifested most conspicuously at North Avenue, which was at one time the northern boundary for Chicago.

THE MYTH DEBUNKED
The townships to the north and south of North Avenue (North Boulevard) were surveyed at different times by different people.

The surveyors who laid out the city south of North Avenue appeared to have been a bit inaccurate. Harlem Avenue, the city’s western border, is 1/16 miles west of where it should be at Madison Street. That's 330 feet. Just guessing, but if one had to hide a 330-foot mistake, they may parcel it out in small increments along the six-mile width.

It's not like this is the only surveyor's error in Chicago. The whole city is 1.3° off true north. As a result, it doesn't square with the survey grid between the Wisconsin boarder and Central Street in Evanston, which was laid out independently.

EVIDENCE
Central and Golf Road are supposed to be parallel. However, if you follow the lines in a Street atlas, you’ll find Central and Golf are 1.5 miles apart in Elgin, IL., but only 1/2 mile apart in Evanston.

At the time of the survey, who cared about such a small difference? They thought they were surveying farm property lines. They couldn’t imagine what the future would bring. 

3 comments:

  1. I'd pick a nit: That 1.3 degree variance is only an 'error' if the surveyors were tasked to lay it out to true North; if they were starting with the extant street grid, the offset was already built in. (And most E-W streets are off by the same amount, right?)

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  2. There is also a misalignmenton north-south streets along the northern Indian Boundary Line. See NWCHS Newsletter (The Central Avenue Jog)

    http://nwchicagohistory.com/pdf/newsletters/jphs-jan2007.pdf

    ReplyDelete
  3. North Avenue is a "base line" in the US Township and Range System. North-South grid lines and streets must be re-aligned versus Polar North at these points lest the streets start converging instead of remaining parallel.

    ReplyDelete

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