Maps: Reference & Communication

Scale - map

Scale

Maps: Two-dimensional, scaled representations of Earth surface - show spatial data (data with locational component)Cartography (map-making) involves 4 design decisions – based on purpose of map

Projection Scale Aggregation Type of Map (thematic* or

reference)

smaller scaleSample Area Covered Fraction Scale Verbal ScaleWorld 1:78,000,000 1 in = 1,250 mi No. America 1:36,000,000 1 in = 570 miCentral U.S. 1: 4,000,000 1 in = 64 miAAA Colo map 1: 1,267,200 1 in = 20 mi

larger scale

Smaller-scale shows more land area in less detail. Used to show global patterns.

Larger-scale shows less land area in more detail. Used on local maps.

Map Scale The ratio of map distance to earth distance, measured in the same units

Displaying the same geographical features at various scales may also depict misleading results.

Percent of 1990 pop age 25+ with bachelor's degree

Data aggregated by State

Map Aggregation The level of detail for dividing a thematic map into

geographic units

Ranges from coarse divisions

(e.g., by countries) to fine divisions (e.g., by zip

codes)

Percent of pop age 25+

with bachelor's degree (1990)

Note what information is lost at higher levels of

aggregation

Aggregated by State

(northeast close-up)

Aggregated by County (WV, MA)

THEMATIC MAPS – depict characteristics of places

Categorical type - Depict areas that are different in kind- Use several distinct colors to show different categories

desert forest tundra

Examples: climates, religionsChoropleth type

- Depict areas that are different in amount- Use shades of similar colors to show different values

high value medium low value

Examples: population density, literacy rates

Example of “categorical map”

Example of “choropleth map”Human Development Index (HDI) Rankings

Includes GNI/PPP, Literacy, and Life Expectancy

Which regions have high HDI?Which regions have low HDI?Which places are exceptions?

Isoline type(Average Daily Solar Radiation)Lines connect points of equal value Dot Density type

(Wisconsin Acreage in Potatoes)

Each dot represents a frequency of mapped

variable

Proportional Symbol Map (Graduated Circle type)

Size of symbol varies in relation to frequency or intensity of the mapped

variable

Proportional Symbol Map (Flow Vector type)