What are the dimensions of Chicago’s street grids, the city rights of way, what are the lot sizes, are the rights of way wider at certain points in the grid design, are there deviations from the grid in particular areas that are observable and consistent in those areas, etc?
For something that is such a popular topic I have never seen so much conflicting information. There are literally dozens of articles online lauding the efficiency of Chicago’s street grid but all their details seem to conflict in important ways.
For example, some say that the grid is based on a 0.5x0.5 mile square while others say it is based on a 1x1 mile squares. From what I have read it seems like the city was originally founded based on 1x1 mile squares originating from the Land Ordinance of 1785, but it seems like since then additional major rights of way have been established every 0.5 miles in both directions (North/South and East/West). Which is it? Is this a regular pattern or does it vary based on area of the city? Is there a difference between the right of way widths from the original Land Ordinance mile roads and the .5 mile roads between them, for example creating a grid with major and semi-major roads alternating every .5 miles in each direction? Or is there a major road every .5 miles and they all have pretty much the same right of way width?
Also, according to what I’ve read, the “idealized” chicago block is 1/16th mile by 1/8th mile with the long end laid east to west to maximize the amount of sunlight that would hit the face of buildings. Why then do such a large minority of blocks, even while most conform to those 1/16th mile by 1/8th mile dimensions, have their long end running North/South?
Also, how do Chicago’s standard lot sizes square with the right of way dimensions? In feet, a standard Chicago city block should be 660’x330’ including rights of way. I have read articles about the Land Ordinance or Public Land Survey System that describe that each block would be surrounded by a 60’ right of way on each side and would have a 20’ right of way running down the length in the middle to provide service access to the rear of lots (forming our alley system). These dimensions make a lot lot of sense because if you ask any Chicagoan they will tell you that the standard Chicago lot is 25’x125’. 330’-60’-20’=250’, divided by 2 gives you 125’ which is the standard lot depth. Perfect. That makes sense. HOWEVER, I have been reading City of Chicago Streetscapes Manuals that describe that the standard street ROW is actually 66’ with an 18’ alley. That adds up to 84’ of ROW for each block, so each lot should only be 123’ deep. Well… what is it? Is “125 feet” just 123 feet rounded up?
66’ is a very standard width of rights of ways. It is based on an old surveying measure, called a rod, with is 16.5 feet in length. Measured from the center of the street to the face of the buildings would be two rods. From this you get a 6’ sidewalk, a 7’ parking lane, and two 10’ travel lanes in each direction. The “two rod” highway is a template used nation wide.
What is likely confusing about Chicago is that it is has absorbed neighboring towns in the past, so the “historical” Chicago street grid will only apply to jurisdictions actually controlled by the city when it was originally laid out.
The US Public Land Survey System established the section lines at one-mile intervals. Farmland in this part of the country, however, was mostly purchased in quarter-sections of 160 acres, or even smaller aliquot subdivisions.
Decades later, county roads were established on section lines, though in Illinois this doesn’t seem to have been done uniformly. A couple of decades later, rapid growth in Chicago prompted subdividers to start creating subdivisions from the prexisting 40-acre and 80-acre farms. A city ordinance still on the book requires streets to be laid out eight-to-the-mile in one direction and 16-to-the-mile in the other. It doesn’t specify orientation of the blocks, and that seems to have been at the subdivider’s discretion, based on where the streetcars ran and thus where he expected the most profit from commercial frontage or corner lots.
The original rectangular survey lines were 1.3 degrees off true north and had other imperfections that eventually make their way down to houselots. So plats show lot dimensions like 121 feet deep, or 24.5 feet, especially at the end of the block. But the general pattern is a 330 x 660-foot block, with 66-foot streets and 16-foot alleys, and 24 x (mostly) 124-foot lots.
As for the arterial streets on mile intervals, that’s mostly a creation of the 20th century. At horse-and-buggy speeds, one street is pretty much like the next. Streetcars began to reinforce the mile arterial pattern, and in some parts of the city a half-mile pattern as well, but in much of the city the half-mile streets are just ordinary residential streets.
I’ll be talking about some of this stuff at a Chicago Architecture Foundation Lunchtime Lecture in October.
as one of the above noted, many of the grid variations came about as Chicago-proper annexed neighboring municipalities (see linked gif) and presumably those smaller villages were more haphazard with their town planning:
I realise now that it was a bit different. If was one of the guided architectural walks that started from the foundation. Before we left the guide spoke a bit about the layout of the city.