A River Runs Through It:

class: center, middle, inverse, title-slide

.title[
# A River Runs Through It:
]
.subtitle[
## The Geography of Income Segregation
]

---

## Question

- Why, anecdotally, does it seem like "the south side" often contains the poorest neighborhoods of a city?

- Is this true generally in the United States?

- If so, *why??*

- Could it have something to do with geographic features?

- People prefer not to be downstream / downwind of manufacturing? 
  
  - If so, we'd expect the poor side of town to frequently line up with the direction of flow of the city's river.
  
---

## Data Collection

<a href="https://www.opportunityatlas.org/">
<img src="img/atl-opportunity.png" style="display: block; margin-left: auto; margin-right: auto; width: 400px"/>
</a>
  
  
---

## Data Collection

In the 50 largest cities in the United States, here's the neighborhood geometry breakdown:

.pull-left[

<br>

|       | Num. Cities|  %|
|:------|-----------:|--:|
|west   |           4|  8|
|center |           8| 16|
|north  |          10| 20|
|east   |          11| 22|
|south  |          17| 34|
]

.pull-right[
**South Side:** Los Angeles, Chicago, Phoenix, San Antonio, San Diego, Dallas, Columbus, Boston, Detroit, Baltimore, Albuquerque, Fresno, Tucson, Atlanta, Colorado Springs, Virginia Beach, Long Beach

**North Side:** New York, Philadelphia, San Jose, Charlotte, Denver, Nashville, Portland, Milwaukee, Miami, Tulsa

**East Side:** Houston, Austin, Fort Worth, San Francisco, Seattle, Washington, Kansas City, Omaha, Raleigh, Bakersfield, Arlington

**West Side:** Jacksonville, Louisville, Memphis, Oakland

]

---

## Data Analysis

How *weird* is it that there are only 4 cities with poor west sides, but 17 cities with poor south sides?

This is where probability and statistics comes in handy.

- Is this a pattern you wouldn't expect to observe by chance alone?

So we create a thought experiment:

![](img/d4.gif)

Repeat that 42 times (one for each city with an obvious geographic divide):

```

east south  west north 
    9    10    10    13 
```

---

## Data Analysis

If you repeat that exercise over and over, generating 10,000 sets of 42 randomly generated cities, how often are there only four cities with poor west sides?

---

## Data Analysis

And what's the chance that you at least 17 cities with poor south sides?

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## Data Collection: River Flow

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## Data Analysis: River Flow

- Are poor neighborhoods more likely to be downriver? We can use similar statistical methods to answer this question.

- To be extra generous to the hypothesis, if a river flows "southwest", I'll count both the south and west of the city as being downriver.

- This means there's a roughly 3/8 chance that river flow and neighborhood orientation line up.

Here are the actual results (out of 39 cities with major rivers flowing through them):

|Downriver? | Num. Cities|
|:----------|-----------:|
|no         |          20|
|yes        |          19|

I leave the full statistical analysis as an exercise to the reader.

---

## Conclusion

- As best I can tell, the poor side of US cities is most likely to be the south side, but not more likely than chance alone would suggest.

- More data and more careful measurement could resolve the question more definitively.
  
--

- There is no clear tendency for the poor side of a city to be downriver.

- There is some [interesting evidence](https://www.theguardian.com/cities/2017/may/12/blowing-wind-cities-poor-east-ends) that cities in England are more likely to have poor *east* sides, perhaps due to the direction of prevailing winds.

![](img/london-east-side.png)