Thematic Cartography

The Cartographic Language

Timothée Giraud

Feb 26, 2025

Cartography

Cartography

Cartography is the discipline aimed at making maps.

Cartography has scientific, technical, and artistic foundations.

Cartography

Scientific foundations

  • Mathematics is one of the pillars of cartography: geodetic systems, coordinate reference systems are fundamental tools for map making.

  • The preparation of maps (data management and transformations) is a process that requires precision and accuracy .

  • The cartographic process is based on a set of rules from the semiology of graphics and on strong methodological tools.

Cartography

Scientific foundations

The map itself is the subject of numerous researches: communication efficiency, animated cartography, optimization of flow mapping…

Cartography

Technical foundations

Cartography is based on the acquisition, preparation and processing of data. It requires the use of specialized software products (spreadsheets, GIS, mapping software, spatial databases…).

Cartography

Artistic foundations

The process of map creation usually involves a search for aesthetics, design, and a certain viewpoint on spatial phenomena.

As with any communication object, the graphic design of a map has an impact on the transmission of the message.

Cartography

Artistic foundations

Frontière États-Unis / Mexique : une fracture humaine et économique (Source : Rekacewicz, 2009)

War Business (Source : Lambert, Zainin, Mad Maps, 2019)

What are the maps used for?

Performative maps (activism, propaganda…)

Region of Rat-Bitten Babies (Source : Bunge W., Bordessa R., 1975, the Canadian Alternative)

Geography of Revolution (Source : Bunge W., 1971) more

What are the maps used for?

Analysis (reveal phenomena and spatial organisation)

Adapted from John Snow’s cholera map of 1854

What are the maps used for?

A planning tool

VGI map of dangerous spots while biking (Source : Fédération des Usagers de la Bicyclette, 2019)

What are the maps used for?

Visualizing its own territory, navigating

(Google) Maps snapshot

Take a step back

The context of production is important.
To better understand the issues of legibility and communication of the cartographic message, ask yourself

  • What is my role in producing a map?
  • What is the purpose of my map, how do I want people to respond to it?
  • Who is the intended audience? What do they need to know to understand it?

This directly influences the *geographic bounding box** and *projection** used, the *generalization** of the map background, the *graphic choices** (fonts, colors, format), the *vocabulary** used.

Take a step back

What about the thematic map?

A widely appreciated tool for analysis, decision support and communication.

It is necessary to identify the graphical means that allow to go from a “simple” spatialized statistical information to an efficient graphical representation.

M A P S !

M for message

The message to be conveyed. The message should be coherent, clear, understandable and as simple as possible so that it can be easily integrated.

A for artistic

A map should be attractive. It should be aesthetically pleasing and well designed.

P for people

The map should be designed for a specific purpose. The mapmaker needs to know whom he/she is addressing.

S for scientific

The map is a professional tool of the geographer. It is a scientific object that follows strict and precise rules, it must be as reproducible as possible and thus open to scientific discussion/dispute.

The Cartographic Language

The Cartographic Language



1. Use the rules from the semiology of graphics



2. Use the cartographic codes and conventions

Semiology of graphics

Jacques Bertin has developed a set of rules for the graphical representation of information.

  • 3 types of relationships within data sets. Maps are created to visualise these relationships.

  • 6 visual variables to transcribe these relationships.

3 types of relationships

  • Differentiation: express relationships of equivalence or difference, with no hierarchy or classification.

  • Order: express a hierarchy in the data.

  • Proportionality: express raw quantities.

3 types of relationships

Visual variables

A visual variable refers to the way in which graphical figures are made to vary in order to visually represent variations in statistical data.

  • size
  • value
  • color
  • shape
  • orientation
  • texture

Visual variables

Localization and positioning

Localization refers to the position of a place on Earth’s surface. It is a geographical notion.

Positioning refers to the graphic transcription of geographical objects on a map using points, lines, or polygons. Is is a cartographic concept.

Absolute quantitative data

ONLY one visual variable can be used to show absolute quantitative data: the size.

It is the only visulal variable that can express differences, hierarchy and above all proportionality.

Absolute quantitative data

Absolute quantitative data

Absolute quantitative data

Emigrants from around the globe (Minard, 1858)

Absolute quantitative data

Interegional Trade. Source: Atlas de l’espace mondial contemporain

Absolute quantitative data

Absolute quantitative data

Paull, J. et Hennig, B. (2016). Atlas of Organics: Four maps of the world of organic agriculture. Journal of Organics, 3(1), 25‑32.

Relative quantitative data

(and qualitative ordinal data)

Relative quantitative data

Relative quantitative data

The choropleth map: A cartographic representation consisting of ordered coloured areas on a grid (e.g. administrative division).

Used with relative quantitative data and ordered qualitative data.

Before the choropleth map…

  • The statistical information in your spreadsheet is not always ready to be mapped.
    The information may need to be converted, collated or reduced to make it understandable.

  • Relative quantitative data (rates, indices, etc.) always need to be synthesised, broken down into classes of values.
    This process is often called discretization.

Discretization

  1. Summarize the statistical series
    • Position parameters (mean, median, mode…)
    • Dispersion parameters (standard deviation, interquartile interval…)
  2. Analyse the distribution
    • Histogram, box plot, distribution chart
  3. Determine class intervals
    • Several methods

Discretization

  1. Classes must be homogeneous and distinct
  2. The number of classes must be smaller than the number of observations
  3. Essential characteristics of the distribution should be preserved (extent, dispersion, shape of the distribution)
  4. Use rounded limits, or use relevant values. Boundary values should be easy to read an remember

Discretization

Discretization

Observed thresholds

Equal amplitude

Discretization

Equal numbers

Standardized

Discretization

Geometric progression

Discretization

Relative quantitative data

Popular instruction in France (Source : Dupin, 1826)

Relative quantitative data

Source : USGS, 2013

Relative quantitative data

Relative quantitative data

Property prices

Relative quantitative data

High Speed rail in Europe, 2016 (Source : Wikipedia)

Qualitative ordinal data

Qualitative nominative data

Qualitative nominative data

Qualitative nominative data

Socio-professional status of property buyers

Qualitative nominative data

Qualitative nominative data

How Hollywood destroyed America (Source : theconcourse.deadspin.com, 2014)

Qualitative nominative data

Qualitative nominative data

To sum up and simplify

Codes & Conventions

Codes & Conventions help contextualize the map.

Mandatory elements:

  • Title
  • Date
  • Legend
  • Source (and author)
  • Scalebar
  • North arrow

Legends

Scale bar

General layout of the map

Cartographic composition

Tips

Credits

Credits

Most of the figures and slides are from:

  • Lambert, N., & Zanin, C. (2020). Practical Handbook of Thematic Cartography: Principles, Methods, and Applications (1st ed.). CRC Press.
    https://doi.org/10.1201/9780429291968

  • The chapter Cartographie thématique et règles de la sémiologie graphique from the course Initiation aux SIG et à la cartographie thématique by Ronan Ysebaert, Maxime Guinepain, Nicolas Lambert, Flora Hayat and Hugues Pécout.
    https://github.com/rysebaert/infogeo