in Geospatial

GIS Notes: Cartography and Chloropleth

Chloropleth maps distinguish classes of data through different colors.

Geoliteracy is increasing; is part of media literacy. Geoliteracy analyses map making techniques, political and ideological agendas, common human error, aesthetic, and communication.


More geospatial data available than any other time. Finding the right data can be hard. Preparing data for use requires skill and patience.

Raw Data

Learn how to make a map from raw data. Apply filters to raw data to reduce the complexity of the map.


Sometimes you get a hard copy and digitize the map by tracing and other techniques.


Metadata is data about data. Metadata tells us where maps come from, what projection they are in, and other details.


The ability to use symbols, maps, diagrams, etc. to effectively communicate.

Map Purpose

Maps are made to communicate ideas


Maps model reality through:

  • Symbolization
  • Simplification
  • Classification


Using visual icons to represent features


Removing features or making data clear


Grouping similar features to reduce complexity

USGS Quads

USGS Quads have been developed for over 150 years


Every map maker has different preferences


Elements of Maps

  • Data, selection, projection, scale, convention
  • Colors
  • Symbology
  • Labeling
  • Arrangement

Try not to intentionally deceive the reader.


“Dangers of defaults”

Tools constrain design, always question default settings.


Idea: design maps for varying media. One map, multiple formats:

  • large
  • small
  • greyscale
  • print


Progressive enhancement for GIS?

e.g. css @media for scalable maps.

Tufte Rules

  • Show the data (show behind the scenes, name sources)
  • Display the data clearly
  • Just enough beautification
  • Try not to distort the data
  • present many numbers in a small space
  • make large data sets coherent, readable, understandable
  • reduce amount of data towards coherency
  • encourage the eye to view the data
  • create levels of detail, broad to fine
  • have a clear purpose, description, extrapolation, tabulation, decoration
  • closely integrate with statistical and verbal descriptions

Self Contained

The map should be useful to a reader even if absent from the original document or context.

Key questions

  • Who are the intended audience?
  • What is the message or story? What is the purpose?
  • Where is the data for the map?
  • How will the final product be displayed and/or distributed? (E.g. 8.5 x 11, ANSI E, B&W?)


Map scale is changing with technologies including web mapping (GIS, online maps, etc.)


Conventions include:

  • Title
  • Caption (state what the map shows)
  • Author, contact info
  • Sources
  • Missing values
  • Legend (all symbols and colors)
  • Scale (e.g. scalebar)
  • orientation (north arrow)
  • Borders and neatlines
  • Outline


  • Emphasize key info.
  • De-emphasize other info
  • create visual balance


The optical center, or where our eyes naturally tend to come to rest, is just above and to the right of the geometric center.

Geometric and Optical Centers

Geometric and Optical Centers

 Golden Ratio

The golden ratio can be expressed as:

A is to B as A + B is to A

Golden Rectangles

Golden Rectangles

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