Comprehensive Study Notes on Introduction to Maps and Geospatial Data

Categorization of Geographic Maps

Maps serve as the primary tools for geographers and are categorized into two generalized types: reference maps and thematic maps.

Reference Maps

Reference maps are primarily informational. They are used to retrieve specific information regarding the location of physical and man-made features on the surface of the Earth.

• Definition and Purpose: These maps act as a point of reference to locate where things are. They provide a general overview of a landscape or facility without focusing on a specific data-driven theme.

• Examples of Reference Maps:

  • World Maps and City Maps: General layouts of continents, countries, or urban streets.

  • Evacuation Maps: Directions for exiting a school or building during emergencies such as fires or tornadoes.

  • Topographical Maps: Specialized maps displaying the elevations of mountains and terrain features.

  • Subway System Maps: Guides for transit travelers to identify specific stops for boarding or exiting.

  • Mall Maps: Diagrams showing the locations of stores and specific facilities like food courts.

  • National Park Maps: For instance, the Glacier National Park map provided by the National Park Service identifies shuttle stops across the park to assist in traversing the area. These lack a specific data "theme" (e.g., they do not show which stops have more wildlife or higher passenger volume).

Thematic Maps

Thematic maps are designed to tell a story or illustrate a specific theme. Unlike reference maps, they focus on quantifiable data that can be numbered or measured.

• Identifying the Theme: The story of a thematic map is typically identified through its title, which acts similarly to the title of a book, revealing the specific phenomenon or data being measured.

• Significance: Thematic maps are the primary focus of geography coursework and Advanced Placement examinations.

• Types of Thematic Maps:

  • Choropleth Maps: These utilize colors or shading to represent spatial data. Generally, a darker shading or color intensity represents a higher quantity or density of the phenomenon. For example, a map of $COVID-19$ cases might show high concentrations in states like New York, Illinois, Florida, Georgia, Texas, and California, while showing low numbers in Maine, Vermont, West Virginia, Montana, and Wyoming.

  • Dot Maps (Distribution Maps): These utilize dots to show the distribution, pattern, or spread of information across a territory. Each dot is assigned a specific value. In a map showing corn harvested for grain, one dot might represent $10,000$ acres. While effective for showing patterns in states like Indiana, Illinois, and Iowa, they are less effective for showing density in highly concentrated areas because dots may overlap (dots on top of dots), making it difficult to quantify exact numbers.

  • Graduated Symbol Maps: These use symbols (typically circles) that change in size proportionally according to the value of the data being measured. For example, a map of airport enplanements might use larger circles for high-volume hubs like Hartsfield-Jackson Atlanta, Dallas/Fort Worth, LAX in Los Angeles, and Chicago O'Hare, and smaller circles for less busy airports.

  • Isoline Maps: These maps feature lines that connect points of equal value. They are sometimes compared to a thumbprint or a "bowl of spaghetti." Every time a line is crossed, the value of the quantifiable data changes. When lines are close together, it indicates the value is changing rapidly; when they are far apart, the value is relatively flat or consistent. While colors are often added to assist in readability, they are not strictly required.

  • Cartograms: These maps distort the physical size of geographic areas based on the value of a specific variable rather than true land area. They are often described as "whimsical," "zany," or "cartoon-like." In a cartogram of U.S. Census population data, populous states like Florida, California, Texas, and New York appear disproportionately large, while sparsely populated states like Montana and the Dakotas may become almost invisible.

Analyzing Data Distribution: Dairy Farms Case Study

Examining a thematic distribution map of dairy farms in the United States provides a practical application of map analysis.

• Map Type: This is a dot map.

• Theme: The distribution of dairy farms across the lower $48$ states.

• Data Key: Each dot represents approximately $10$ dairy farms.

• Concentrations: Significant clusters are visible in Pennsylvania, Ohio, Indiana, and particularly Wisconsin (a state culturally associated with dairy, such as the "cheese head" tradition among fans of the Green Bay Packers).

• Low Density Areas: The map reveals a lack of dairy farm concentration in the Deep South, Texas, the Desert Southwest, the Mountain West, and the Great Plains.

Analytical Framework for Geographic Study

When evaluating any map, students of geography should utilize a specific set of critical thinking questions:

1. Map Identification: Is this a reference map or a thematic map?

2. Purpose: What specific kind of information is being presented?

3. Data Analysis: What is the quantifiable data intended to be seen on the map?

4. Selection Rationale: Why did the mapmaker choose this specific style of thematic map (e.g., choropleth vs. cartogram) to represent this particular set of information over a different format?