Maps, Truth, and Cartography

HES 505 Fall 2022: Session 24

Matt Williamson

Objectives

By the end of today you should be able to:

  • Describe the various elements that comprise a map

  • Articulate common pitfalls that lead to misleading maps

  • Describe and generate several common types of data maps

Map Elements

Scale

  • Relates map distance to distance on the ground

  • Ratio scales (1:24,000 or 1/24,000)

  • Graphic scales

  • Large vs. small-scale?

Projection

Developable Surfaces

  • Distortion makes scale invalid across large areas

  • Distortion increases with distance from standard line

  • Five distortions: areas, angles, shapes, distances, and direction

Map Symbols

  • Graphic code for retrieving information

  • (De-)emphasize (un)important information

  • Contrast and the role of colors

Generalization

A good map tells a multitude of little white lies: it supresses truth to help the user see what needs to be seen…
— Mark Monmonier

Geometry

Zhilin et al. 2008

Context

  • Filter out irrelevant details

  • Two elements: selection and classification

  • Reflect interpretations of the relative importance of different features

Mackaness and Chaudry

Data Maps

Point Maps

  • Dot Maps: quantity represented by amount and concentration of dots

  • Proportional Symbol Map: Geometric symbols scaled in proportion to a quantity

Ebbinghaus’ illusion

::: columns ::: {.column width=“50%”} ::: ::: {.column width=“50%”}

Line Maps

From High Country News

Choropleth maps

Example

Cartograms

Example