Purpose: Quantile mapping is a method of graphically depicting statistical data by dividing the geographic information into rank-ordered categories (or quantiles) where each category has an equal number of geographic units (in this case, states). This method enables you to compare maps of different variables for relationships.

Geographic Standards: The geographically informed person knows and understands:

Standard 1: How to use maps, and other geographic representations, tools and and technologies to acquire, process, and report information from a spatial perspective

Standard 3: How to analyze the spatial organization of people, places, and environments on Earth's surface

Standard 9: The characteristics, distribution, and migration of human populations on Earth's surface

Standard 12: The processes, patterns and functions of human settlement

Standard 17: How to apply geography to interpret the past

Materials:

1. Population Data Tables from GAW packet (pg 18,19)
2. Population data sheets
3. Blank maps of different continents; & map from back of GAW book
4. Quantile Data table
5. Pencil/pen
6. Same 5 Colored pencils/markers for each group

1. Divide the class into groups of 4-5 students and provide each group with a blank outline map, a quantile data table, and an identical set of 5 color pencils/markers.

2. Ask each group to choose different topics for purposes of later comparison or choose a number of topics (data items) equal to the number of class groups. Teacher should pick a topic and map it together on the overhead projector before setting students to work in groups.

3. Ask each group to rank a different data item from the highest value (1) to the lowest (50 or 51 states). Use Quantile Data Sheet.

4. Determine the number of categories (quantiles) to display. The general rule of thumb is 3 to 7 categories. Five categories work well when mapping the data for the 50 states/51 (DC) since they allow for 10 states per category (except in the case of tied rankings). In using five categories, simply count 10 states down from the top, then another 10, and so on. Just as long as there is an equal (or close to equal) number of geographic units in each quantile.

5. Direct the groups to transfer their data to the maps. To allow for consistent comparisons, have each group use the same colors in the same order to represent their specific categories. Dark to light colors work well.

6. In completing the maps, the class must deal with issues of titles, notes and legends.

7. Display the maps and ask the students to look for geographic patterns and relationships. Develop geographic questions for your map. Wonder and Discover type questions to discuss and analyze the data you see.
   • What is the pattern of the relationships between maps?

Extensions: Use the World Population Data Sheet to look at other regions of the world in the same way with quantile mapping.