Mapping the Number of Legislators by State vs The Number of Legislators Per Resident by State

My mapping challenge for today is to make a choropleth map. I enjoy the challenge presented by making these kinds of maps. I find that often times when I make them, they require a lot of fine tuning before they are “done”. What is perhaps most interesting about these kinds of maps is that they can show the same set of data very differently, depending on how a mapping subject is framed, what statistics are incorporated, and what symbology choices and data classification methods are used. This is important to note because choropleth maps may help persuade a reader one way or the other about a certain topic. For example, if five different cartographers attempted to map median household income for the same state using the same population and income statistics, they are likely to produce 5 different maps.

To demonstrate this, for today’s project I decided to map political representation in the United States. I created two maps, using the same data, but framing my approach and subjects for each map slightly differently. One map explores the total number of legislators per state, while the other shows the number of residents per legislator. I detail my approach below.

Approach

First, I needed to pull in data. For both maps, I used a shapefile of the United States that showed state boundaries and included state population demographics from the US Census Bureau’s 2017 American Community Survey’s population estimates embedded within its attribute table. I added a new column to the attribute table to include the total combine number of state legislators (state senators + state representatives, or their equivalents). To get this data, I referred to a list of the total number of legislators by state published by the National Conference of State Legislatures. In gathering this data, I was surprised to learn that New Hampshire’s legislature, the New Hampshire General Court, which is comprised 424 members, is the third largest legislative body in the in the English-speaking world, behind the British Parliament and the U.S. Congress.

Map 1: Number of Legislators by States

Once I had my data prepped, I got to mapping. My first map was straightforward enough, as it was limited to only including a count the total number of legislators per state. In exploring the data, I learned that New Hampshire, with its combined 424 legislators, has the most legislators of any state and Nebraska, with only 49 legislators (senators), had the fewest. Also of possible interest, Nebraska has the only unicameral state legislature in the United States. The mean average number of legislators for all states is 147.7 and the median average is 142.5.

Using ArcGIS Pro’s symbology pane, I used the graduated colors symbology type to start making a choropleth map and selected standard deviations as my data classification method, incorporating a 1 standard deviation interval size. This method shows how much a value varies from the mean average (or center). In this case, it this method will show how far, either above or below, from the mean of 147.7 legislators each state’s number of legislators falls. This seemed like an appropriate data classification method for this map. Below is my resulting map.

In revewing the map, I was not expecting New Hampshire, which is realitvely small in size and population (with just 1.36 million residents) to have the most legislators. After learning that it was the third largest legislature in the English-speaking world, I shouldn’t have been surprised. I also noted that California, which is the third largest state in area and largest in population, only has 120 legislators. It is also curious that states with simliar poplations can have very different numbers of legislators. For example, Wyoming has a population of 581,075 residents and Vermont has a population of 623,251 residents. They rank 50th and 49th in terms of population, respectively. Wyoming, which is smaller in terms of population, has just 90 legislators, while Vermont has 180 legislators, double the amount. Why? Becuase, to paraphrase former US Supreme Court Associate Justice Louis Brandeis, each state is its own labratory of democracy. While it is interesting to compare raw counts of legislators by state, what if we re-frame the question by asking what a state’s ratio of residents per state legislator is? How different would that map look? This is the focus of my second map.

Map 2: Number of Residents per Legislator

For my second map, I decided to use the same data, but this time I incorporated the American Community Survey 2017 population estimates and calculated the number of residents per legislator. One caveat I want to note here is that the US Census Bureau has released its 2020 population figures, and the data I am using is a little outdated. Still, I expect that it should remain fairly accurate.

To calculate this ratio, I took the total number of residents in each state and divided that figure by a state’s total number of legislators. The result was the number of residents per legislator. In choosing my symbology, I followed the same approach used in my first map, keeping the standard deviation data classification method. Below is my resulting map.

Unsurprisingly, states like New Hampshire and Vermont have a comparatively low number of residents per legislator. The mean average number of residents per legislator is 45,012.90 residents while the median average is 32,590.5 residents. New Hampshire had the smallest figure, with just 3,217.6 residents per legislator, while California had the highest, with 330,094.1 residents per legislator. The range displayed here is astonishingly big.  

One could interpret this map as showing that residents of states with a low number of residents per legislator like Vermont and New Hampshire as having more political power than the residents of states with a high number of residents per legislator like California and Texas. The idea anchoring this perspective is that power becomes more diluted as the number of residents represented by a single legislator increases. Conversely, the more representatives a state has, the less power each representative wields. The map sparks some interesting questions about political representation in the United States.

Both maps, while working with the same datasets, show different phenomena based on the questions that each map was trying to address. One thing I touched on above but did not demonstrate in the mapping examples here is that the method a cartographer uses for data classification can completely change the map. I stuck with standard deviations because I wanted to place a visual emphasize of divergence from the mean, but I could have just as easily gone with a different method that would have resulted in a similar, but different map. If you ever see choropleth maps out in the wild, always interrogate them and question your initial gut reaction assumptions.