Monday, April 29, 2013

Mapping Z Scores

Z Scores can be an easy and effective way to organize and analyze a dataset with problematic measures of central tendency. Z scores, also known as standard deviation units, demonstrate how far away (positively or negatively) any given data point is away from the mean of that data set. You could just show the difference between the data point and mean, in the original units, but that might not give you as clear a picture of how just how much that point differs from the central tendency.

Take population growth by Virginia county for instance: According to the American Community Survey's 2012 data, most counties are adding people, but some are losing residents. In fact, there's a huge range in population change. Henry County, for instance, has lost 1,185 residents in between 2009 and 2011. Fairfax, in northern Virginia, gained over 36,000 people.

We have also have a significant positive skew here. Look at how much larger the mean is than the median in the below SPSS output:
In fact, only a handful of counties greatly affect the central tendency of the dataset (Surprise! They're in Northern Virginia). The graph below shows how three counties spike far above the generally stable cluster near the x axis.

So the mean and median isn't helping us very much figuring out population change in Virginia. The "average" county isn't adding 1,379 people annually, as the mean would suggest.

That's where measures of dispersion help a lot. SPSS already gave us the standard deviation, so we just take subtract the mean from each value and divide by the standard deviation, and we have Z scores for each county.

Join those Z scores to a shapefile of Virginia, classify under natural Jenks breaks, and voila:

I've been doing a lot of thinking about the Virginia Gubernatorial Race and the changing demographics of the state. And looking at a map like this demonstrates that Democrats really don't need to compete throughout the state in statewide races. They can win by continuing to shore up Northern Virginia, and will continue to with these population changes. Not a bad plan, unless you want to win back the state senate.

Map of D.C.'s Rooftop Bars

Some folks over at the D.C. Reddit group have been trying to compile a complete list of the city's rooftop bars, and someone asked for a map. So here you go:

Friday, April 12, 2013


If you got a job last month, congratulations. You were one of a very lucky 0.75% of people who wanted one too. Not as bad as the lottery, but not a recipe for prosperity. 

A Lost Economic Generation?

Young people have it pretty rough in this country right now. Most age groups and demographics do too, but the statistics are worth taking a closer look at:

  • Median net worth of people under 35 fell 37% between 2005 and 2010; those over 65 took only a 13 percent hit.
  • The national unemployment rate is 7.6%; For people between 20-25, it's 13.3%. For 18-19 year olds, it's 22.1% (remember these percentages aren't out of the total population, but rather the portion of the age group that are actively seeking work but can't find it.  And as this post from Young Invincibles points out, that $4.25 an hour internship or 20 hour a week bartending gig means, that in the eyes of the Bureau of Labor Statistics, you are very much employed.)

Why should we care? Aren't the young less likely to have obligations like mortgages, children, and aging parents? Take a look at this chart that shows how rising costs in education and health care, combined with sluggish earnings trend, is putting extra financial pressure on the nation's young people. 

As the gap between the top green line and the other three shrinks, young people will delay moving out on their own, making major purchases, and also be more willing to work those low paying jobs that America's hirers are more than happy to keep them in. 

For each year lost to unemployment, not only is that a year of forgone cash earnings, that are very likely to be spend to spur the economy as a whole, but it acts a drag on future earnings as well. Even with a more significant economic recovery, the lack of gained experience and skills could amount to a $20 BILLION LOSS  in earnings over the next decade. Of course that's lost taxable income as well, so advocates protesting the President's proposed cuts to safety net programs should probably consider advocating investing in the generation that's responsible for the tab of those benefits. 

Friday, April 5, 2013

What D.C. Neighborhoods Could Use a Metro Station?

The D.C. Metro system is perilously close to capacity, with supply of trains and stations already not meeting demand. Total trips are down slightly this year, but population growth projections as well as growing trends in area residents preferring mass transit to owning and driving their own cars, has spurred the Washington Metro Area Transit Authority to plan expanding the Metro system. A new 49 page strategic plan calls for building new tunnels through the city, a new tunnel under the Potomac River, and a pedestrian walkways between Metro Center and Gallery Place, and Farragut West and Farragut North, and a new station for the Pentagon.

Combine this expansion with the Silver Line and street cars, it's an exciting time for D.C. mass transit. So H Street and Tyson's Corner get their new transit assets, but what about other areas of D.C.? Particularly, what high density residential areas aren't currently served by Metro?

The D.C. Data Catalogue has existing landuse data on every block in the city. By projecting medium and high density residential areas, we can use ArcMap's measuring tool to see what neighborhoods are situated a mile or more from existing Metro stations. 

How about a Gold Line starting in Mclean (a future silver line station), continue northeast to Glover Park and connect to Van Ness on the Red Line, then serving Brightwood, before turning South and connecting to Georgia Ave, a new Crestwood Station, and continue on down to the New York Avenue station.

On its way Southeast, this Gold Line could also service the burgeoning H Street corridor with its connections to the proposed streetcar, before crossing the river and serving multiple neighborhoods in Southeast. The city is more connected, congestion declines, Mayor Gray's "One City" vision realized...

One can dream...

Monday, April 1, 2013

What a 50 Mile Evacuation Zone Means For Virginia and D.C.

It's been two years since the 2011 tsunami and 9.0 earthquake that devastated Japan and wrecked the Fukushima nuclear power plant. Fortunately, the World Health Organization released a report this month concluding that negative health effects from the released radiation would be minimal or not observable.

Louisa County, Virginia, near where I grew up and the family farm still operates, was the epicenter of a smaller 5.8 magnitude earthquake in August 2011. Near by are two nuclear reactors at Lake Anna. After the quake the plant's safety measures worked, and no radiation was emitted. But according to the Nuclear Regulatory Commission, the Anna reactors face an annual 1 in 22,727 chance of the core being damaged by an earthquake and exposing the public to radiation. 

Dominion Power, the company that operates the plant, said that Lake Anna was built to withstand a 6.2 earthquake. The Richter scale is logarithmic, meaning that increases at the top of the scale are more dramatic than at the bottom. Even so, it would seem that the 2011 quake was cutting it close to Lake Anna's limits. 

Two other nuclear plants in the area could also pose a risk in the event of a strong earthquake, Surry Nuclear Power Plant in the Tidewater region and Calvert Cliffs in Maryland, southeast of Washington D.C. 

Drawing a 50 mile radius around each plant demonstrates the cultural, national security, and of course population assets that would be caught in the evacuation zones.

Why 50 miles? Transcripts released last year revealed that the Nuclear Regulatory Commission (NRC) thinks that a 50 mile evacuation zone would be appropriate for a disaster along the lines of Fukushima. Then NRC Chairman Gregory Jaczko also urged Americans living within 50 miles of the plant to evacuate. It turned out that the cooling pools had not completely evaporated as previously thought, but the comments raised alarm in energy and environmental community.

Below is a national look of all the nuclear reactors in the country, with a 50 mile buffer shaded around them.

Key Takeaways:
  • Earthquakes pose a threat to our nuclear power plants, most of which were built when Jimmy Carter was president
  • Many environmentalists say it will be impossible to cut emissions from fossil fuel sources to combat climate change without expanding our nuclear profile
  • After Fukushima the body in charge of regulating domestic nuclear energy production re-evaluated their evacuation zones to fifty miles. Highly valuable national assets are within these fifty mile zones. 
More questions than answers. But laying out the problems ahead is the only way to make well-informed decisions.