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Trivia Teaser - That little bend in the road, down thar

Question: Why is it that when you are flying over the Midwest, you'll see an endless rectangular array of roads neatly arranged in a grid, but every so often, one of the north-south roads will jog just a bit eastward or westward before resuming its northerly (or southerly) course?

A) In the mid-nineteenth century, many states established their own departments of land management, each of which began their surveying at different points. The techniques of surveying were not as accurate as they are now, and when one southerly section line didn't quite met up with another running northward, the two teams ignored the discrepancy, and joined along an East-West line.

B) because the earth isn't flat

C) This is in fact an illusion. The vast majority of rural intersections throughout the Great Plains do not, in fact, meet at right angles, nor at neat four-way corners. We see only a rough peripheral image of many squares at a distance and our brains 'arrange' and integrate this information into a more orderly image, which is easier to remember. It is the same sort of thing that makes a 'vector' graphic take up far less space than a raw 'bitmap'. Our brains work the same way. Such 'jogging intersection' exceptions that we may sometimes notice are actually more the rule.

D) It means that there was probably an obstruction at that point, such as a stand of trees or a lake, which was simply sidestepped when the road was first built, or possibly you are seeing a state boundary that does not fall on a township line.
Question: Why is it that when you are flying over the Midwest, you'll see an endless rectangular array of roads neatly arranged in a grid, but every so often, one of the north-south roads will jog just a bit eastward or westward before resuming its northerly (or southerly) course?

A) In the mid-nineteenth century, many states established their own departments of land management, each of which began their surveying at different points. The techniques of surveying were not as accurate as they are now, and when one southerly section line didn't quite met up with another running northward, the two teams ignored the discrepancy, and joined along an East-West line.

B) because the earth isn't flat

C) This is in fact an illusion. The vast majority of rural intersections throughout the Great Plains do not, in fact, meet at right angles, nor at neat four-way corners. We see only a rough peripheral image of many squares at a distance and our brains 'arrange' and integrate this information into a more orderly image, which is easier to remember. It is the same sort of thing that makes a 'vector' graphic take up far less space than a raw 'bitmap'. Our brains work the same way. Such 'jogging intersection' exceptions that we may sometimes notice are actually more the rule.

D) It means that there was probably an obstruction at that point, such as a stand of trees or a lake, which was simply sidestepped when the road was first built, or possibly you are seeing a state boundary that does not fall on a township line.

Answer: It's choice B, and it's really because the Earth isn't flat, as dumb as that sounds. First, we need to learn a little history. Up until about the time of the Revolutionary War, when land was parceled out, sold, or granted, its dimensions were described by a system of 'metes and bounds' still recently in existence in many states east of the Appalachian Mountains (as well as in Texas). This method begins with a known landmark, and then follows a line according to either a magnetic bearing, the course of a stream, or the track of an ancient highway. As you might expect, this plan has resulted in endless confusion and litigation. As almost any air traveler has noticed with the most casual glance out the window, most of the rest of the country westward of the Appalachians is arranged in a considerably more orderly fashion, as evidenced by patchworks of cultivated fields and the orderly arrangement of parallel and perpendicular country roads which, when they meet, do so at right angles.

This system began with the Land Ordinances of Congress in 1785 (and 1787) which set forth how the Northwest Territory was to be surveyed and established a huge rectangular network of reference lines. Known as the Rectangular System, all its distances and bearings are measured from two primary reference lines which are at right angles to each other. These are the so-called principal meridians, running North and South, and the base lines which run East and West. Starting at the principal meridian and parallel to it at intervals of six miles both eastward and westward are additional north-south 'range' lines. Likewise, starting at the base line and parallel to it at six mile intervals are east-west lines designated as township lines. The crossing of these township and range lines form square 'townships' (as you might guess) which are each supposed to be six miles square. Each one is 36 square miles, each of which is called a 'section' and in turn contains 640 acres of land. Because of the inescapable fact that meridians of longitude converge towards the poles, the actual width of each township along the township line at its northern border is just a smidge less than its southerly width, and it was decided that a correction would be made, every four rows of townships northward of the base line, at which point the six-mile wide townships would be reestablished as if nothing had changed. These jogs that you may see anywhere between Pittsburgh and Denver are indeed such 'correction lines' although their abrupt changes of direction may sometimes be smoothed into gentler curves for today's traffic. The amount of such a sideways jog will increase with latitude. At 30 degrees North, it would only be about 386 feet. At 45 degrees North, it becomes 545 feet. At 60 degrees North, it would be 667 feet (although that's a tad academic considering the northward extent of the continental US).

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