Wednesday, June 19, 2013

Show & Tell for Module 8: Election Data

In this "Show & Tell" session, I'll show you some useful things that were not included in  LAD module 8.

If you'd like you can try these yourself. The data is included in the Challenge8 zip file which you can download and unzip. Here are the notes to re-create what I show you.



The State of Hawaii Office of Elections works with County Clerks to conduct elections in Hawaii. These elections are for Federal, State and County offices as well as other issues that voters decide. Hawaii is divided into precincts to facilitate managing an election and reporting the results. Most precincts have a polling place where voters come on election day to cast their ballot. Schools are often used as polling places which is one of the reasons you get a holiday on election day. Precincts with few voters don't have a polling place and instead vote an absentee ballot.

Here is a map of the precincts in Maui County.

Every precinct has a unique identifier, called a DP. For example, the area around Hana is precinct 13-03. Let's look at the feature table.

You can see that each feature has its DP designation. "PollingPlace" is the name of the place where ballots are cast on election day. "BallotType" shows the combination of Federal Congress (US2), State House (H08) and State Senate (S05). Maui does not delineate County Council districts based on population, so every ballot lists all of the County Council races, thus all end in "MAU". Hawaii and Honolulu do have population based Council districts so their BallotType would show those Council numbers.


Voters are assigned to a specific precinct depending on where they live. Some precincts have a large percentage of voting age population registered to vote, others have less. The State Office of Elections wants to map which precincts have high percentages and which have low.

You've already seen how census block data records the total population and voting age population. From redistricting we know which census blocks make up which precincts so it is easy to summarize and obtain the total population and total voting age population in each precinct. These results have been combined with the number of registered voters in each precinct in this table:

You can see that the DP field is common in both tables so that is a good field for establishing joins and relates. The fields are pretty self-explanatory. "Pop2010" is the total population from the 2010 census. "VAP_2010" is the total voting age population (age 18 years and older) from the 2010 census. "RV_20130513" is the count of registered voters on May 13, 2013.


Here is a handy way to navigate between the different precincts using Data Driven Pages (DDP). The DDP toolbar looks like this:

At first most of the buttons are not active. Click the button on the left of the toolbar to set up DDP.

Fill out the Definition page as shown here. Basically you are saying to use the features in the "precincts_Maui" layer to define a page, one page for each feature. There are other options but let's keep it simple for now. Click the "OK" button.

You'll see that your map has panned and zoomed automatically to the first page based on the first feature, precinct 08-01.

You can click the right arrow... advance to the next page. This page is based on precinct 08-02 so it again automatically pans and zooms such that 08-02 is in the center of the page and fills most of the page.

This is a very handy way to move between features, just configure DDP using that feature class.


Another huge benefit of DDP is with layouts. In LAD module 8 you learned about layouts for making presentation maps. You can design layouts that will change page to page using DDP. You design your layout like you learned already, but you can also insert special Dynamic Text boxes that will display attributes for the current DDP page.

You insert a Dynamic Text box based on a Data Driven Page Attribute. Here's an example:

You can see that I have inserted five special text boxes, one a title box that shows the DP of the current page. The other four show four different values from the table for that feature. This is a very powerful tool for making presentation maps and map books.

You will need to use this precinct data for Challenge 8.

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