Lesson 6 Lab

Proportional Symbolization

In Lab 6, we will explore two symbolization methods for data that are considered discrete and abrupt. Proportional and range-graded symbols are two approaches to represent discrete and abrupt data using symbols that are scaled according to the individual data values. Proportional symbolization scales each symbol size in direct relation to each data value. For example, if you had unique data related to all 88 Ohio counties, there would be 88 symbols of different sizes on your map. A commonly used symbol is the circle. With range-graded symbolization, the data are classed into finite classes. This approach mirrors what you experienced in Lab 5 with the data classification for data for choropleth mapping. This method is also known as graduated symbol (which is Esri-speak). Both range-graded and graduated are a bit ambiguous. A better term would simply be classed proportional circles, but that is probably too long.

In addition to the proportional and range-graded symbolization methods, we will also examine a symbolization method mapping qualitative data via the choropleth method. This method, known as chorochromatic symbolization, is useful when you wish to map qualitative data using the choropleth method.

As a cartographer, you will often have to choose between which approach is better for your data. Essentially, consider the use of proportional symbols when the recovery of the original data values is important. Proportional symbolization method is appropriate for a dataset whose range is not excessive. In such cases where the range is great, extremely large or small symbols could result. Range graded symbolization addresses datasets with large ranges by setting a fixed number of symbol sizes according to a classification method applied to the data. As with other options in the map-making process, the choice between using proportional symbols and range-graded symbols depends on the map's purpose and data characteristics.

In Lab 5, we used data from the American Community Survey, provided by the US Census - a commonly used source of geospatial data for statistical maps. In this lab, we use the same data source, but you also will have the opportunity to choose your own data for this assignment.

The first part of Lab 6 will focus on searching for and downloading data from the US Census Bureau’s data explorer website. This website offers access to all census data collected since 1990 – both at the decennial census and the one- and five-year estimates from the American Community Survey. The second part of the lab allows you to explore using proportional symbols to map your chosen census data. The third part of the lab allows you to explore using range-graded symbols to map your chosen census data. The second and third parts will take place in a new mapping application – Tableau.

This lab, which you will submit at the end of Lesson 6, will be reviewed/critiqued by one of your classmates in Lesson 7 (critique #4).

Lab Objectives

• Create three (3) maps of county-level data from a state of your choosing, sourced from the US Census Bureau. The state must have at least 30 counties.
  • One map must use proportional symbolization.
  • One map must use range-graded symbolization.
  • One map must use chorochromatic symbolization (using a qualitative variable extracted from the census data).
• Learn how Tableau can be used to create interactive maps.
• Calculate class breaks for the range graded symbolization using either quantiles, equal intervals, natural breaks, or mean-standard deviation.
• Understand the impact of different symbolization approaches on the information illustrated on each map and be able to reflect upon and write about these decisions.

Overall Lab Requirements

For Lab 6, you will create three (3) maps, each of which should be created as its own sheet in Tableau. In total, you will have three separate Tableau sheets. You will also write a short reflection statement about the map creation process in Tableau.

• Prepare visually balanced layouts for each map with all required elements suitably sized and balanced negative space.
• Create an effective design for the visual hierarchy: overall title, subtitle(s), legend title(s), legend class labels, metadata (data source/year, your name, and date of completion). Use thoughtful and efficient wording when labeling map elements.

Map Requirements

Map One: Proportional Symbols

• Choose a census variable of interest to map from the provided American Community Survey (ACS) data. As a hint, choose a variable from the 5-year estimate to download.
• Use Tableau to complete all cartographic work.
• Using Tableau,
  • choose an appropriate symbol (e.g., circles, squares, etc.) for this map
  • attend to the design aesthetic of the basemap, county outline fill, symbol fill, and symbol outline colors
  • create a descriptive map title, subtitle, and legend title
  • add metadata to the map that reports on the data source and year, your name and date of map completion
  • include a legend and legend title (note that Tableau is not very flexible in altering a legend for proportional symbols with a large number of mapped features)

Map Two: Range Graded Symbols

• Using the same census data that you did for map one, use range graded symbolization.
• Choose a classification method to determine the class breaks. The available methods include equal interval, quantile, natural breaks, and mean-standard deviation. The choice of the method is up to you but make sure the method is appropriate for the data distribution that you are mapping.
• Use Excel to assist in the following:
  • create a dot plot as you did in Lab 5 to see the distribution of the data for this map
  • include a screenshot of your dot plot with lines manually drawn to demonstrate the breaks you identified
  • identify the data classification you selected and why you thought it appropriate.
• Using Tableau,
  • choose an appropriate symbol (e.g., circles, squares, etc.) for this map
  • apply the data classification limits to the data
  • attend to the design aesthetic of the basemap, county outline fill, symbol fill, and symbol outline colors
  • create a descriptive map title, subtitle, and legend title
  • add metadata to the map that reports on the data source and year, your name and date of map completion
  • include a legend and legend title (the legend for this map will be better designed since you are mapping classes rather than the number of mapped features)

Map Three: Chorochromatic Map

• Using the same census data that you did for map one, derive a single qualitative variable of interest related to the data chosen for maps one and two.
• Using Tableau,
  • choose an appropriate qualitative color scheme for this map
  • attend to the design aesthetic of the basemap, symbol fill, and symbol outline colors
  • create a descriptive map title, subtitle, and legend title.
  • add metadata to the map that reports on the data source and year, your name and date of map completion,
  • include a legend and legend title (note that the legend for this map will be better designed since you are mapping qualitative data with a limited number of categories)

For additional assistance, explore the Lab 6 Visual Guide and utilize online tutorials and training materials such as those listed below:

• Tableau 10 Essential Training. Your access to LinkedIn Learning (aka Lynda.com) is provided through your Penn State login
• These two links are tutorials provided by Tableau
  • Build a Simple Map
  • Customize how your Map Looks

Reflection Statement

Include a short write-up (< 250 words) that includes the following commentary:

• State the variables you used to create the proportional/range-graded symbol map and the chorochromatic map
• For the range graded map, comment on the overall distribution of the data as shown on the dot plot (normal, positively skewed, negatively skewed)
• State the classification method you selected and why (relate this discussion back to the data distribution and what information you intend for the map to portray – remember the concepts from Lesson 5)
• Explain why you chose and how you derived the qualitative variable of interest for your chorochromatic map
• Comment on two (2) positive aspects of working with Tableau
• Comment on two (2) aspects of working with Tableau that were challenging

Lab Instructions

The data for this lab will be self-selected from the US Census Bureau’s data explorer website. Details on how to access this site, how to search for data, and format the data for download will be presented in the Lesson 6 Lab Visual Guide.

Grading Criteria

Registered students can view a rubric for this assignment in Canvas.

Ready to Begin?

More instructions are available in the Lesson 6 Lab Visual Guide.