GeoNet 2: Histograms
by Patrice St. Peter
After this lesson, students will be able to:
(Numbers below correspond to the Minnesota State Learner Outcome List in geography.)
2. Identify and define conventional map symbols.
9. Read and understand the symbols used on thematic maps (e.g., find the height of the
ground from a layer-tinted map; interpret simple relief maps; read heights and identify
slopes, hilltops and valley floors).
14. Describe a distribution shown on a map in terms of density, directional alignment
spatial concentration, gradients and pattern.
15. Interpret pictorial, shaded-area, proportional-symbol, isoline, choropleth,
flow-line maps and cartograms.
20. Explain some of the factors that influence the choice of projections for particular
mapping tasks (e.g., equal-area for population distribution).
21. List some major sources of geographic data and briefly describe their
characteristics (e.g., aerial photographs, satellite images, field surveys,
topographic maps, census records, statistical abstracts, almanacs, questionnaires).
22. Identify the major kinds of symbols used by cartographers and describe the kinds
of data these symbols are usually used to depict (e.g., pictorial symbols, graduated
circles and other proportional shapes, dots and other repetitive symbols, nominal
lines, flow lines, shaded areas, and choropleth shading).
23. Explain some ways in which a cartographer can transform data to make it more
useful for a particular purpose (e.g., calculating percentages of a total, densities
per unit of area, values per capita, or other ratios of several kinds of information).
24. Describe key aspects of the human visual system and show how some kinds of
optical illusion can affect the way people see maps (e.g., red colors for emphasis,
upper-left focus for important ideas, weak grays to minimize clutter in background
25. Identify some ways in which a cartographer may intentionally or accidentally
mislead a map reader (e.g., colors that a significant fraction of the population cannot
discriminate, projections or symbols that distort in order to persuade).
26. Outline the basic components of graphic communication.
28. Classify geographic data into categories for further analysis or graphic display.
This involves selecting criteria for classification and then applying those criteria to
put individual observations into appropriate groups.
30. Select appropriate charting or graphing techniques for the display of information
about a place [e.g., a) Pie or bar charts to show proportions of various features in a
place; b) line or bar graphs to show trends through time in a place; c) bar graphs to
show comparisons of several places; d) line graphs to show differences from one place
to another; e) scatter diagrams to show relationships among features in a place; and f)
graphical analyses to identify exceptions to rules about places].
37. Create a well-designed map layout that includes the title, scale, orientation,
and relative location in the surrounding area (e.g., city, state, country, or globe).
Time Needed: 1-2 class periods
Overview: Students will learn how to create categories for thematic maps using
histograms. This is lesson two in a unit of four lessons that, when used together,
comprise a several day unit on cartography.
Objectives: Students will be able to:
1. Prepare a histogram of data.
2. Prepare three different classification schemes for the same data set.
1. Data Sheet: MIGRANTS INTO THE SUBURBS sheet (this sheet contains an example
of a histogram and three different ways the data can be categorized; see Extra
2. Grid Sheet (see Extra Resources; one per student)
3. Student worksheet (see Extra Resources; one per student)
4. Maps: U.S. FOREST LANDS, 1980 and PERCENT FOREST, U.S. 1980 (see Extra
1. Develop examples of ways the histogram can be divided, using the examples
2. Gather and prepare materials.
1. Handout MIGRANTS INTO THE SUBURBS, Student Worksheet, and Grid Sheet.
2. Have students study the data set showing the migration to the suburbs in the Twin
Cities. They should focus on the last column of figures which shows the percent of
total migrants into these communities that came from outside of the county. That set
of data will be used to illustrate the histogram making process.
3. Students should find the highest and lowest number in the set. Then, they should
subtract the lowest from the highest on the data set to determine the range of
numbers that they will use on the historgram or number line.
4. After sectioning off the number line by 5s (5, 10, 15, 20, etc.) students then put
an _X_ on the number line for each number in the data set. This exercise allows
students to see the spread or range of data and anticipate the categories for a
5. Students should then study their finished histograms for highs, lows, or natural
gaps or breaks in the distribution of numbers shown by all the _X_ marks.
6. Students use the number line to produce three classification schemes for the same
data set or histogram. Students will write these classifcation schemes on the Student
Worksheet. Examples of three classifications are shown on the data set.
7. Students should then select a color scheme or pattern for each category. Remind
students that the least value on a map is shown with pale/light colors or soft
patterns. The larger values are shown with dark/bright colors or intensely bold
patterns. Students may select one color (red, for example) and use varying shades of
intensities for each of the categories.
8. Collect histograms and Worksheet. Students will not map this data.
Students should has divided their histograms into three different classifications.