Cartographic%20Principles:%20Map%20design

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Cartographic Principles Map design
MSc GIS GIS Algorithms and Data Structures

• Martin Dodge
• (m.dodge_at_ucl.ac.uk)
• Lecture 3, Tuesday 11th November 2003
• http//www.casa.ucl.ac.uk/martin/msc_gis/

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Map saturated world

• more maps are available than at any time in
  history
• finding the right map can still be hard
• distribution of map coverage is uneven
• sources of hardcopy maps. dont forget map
  libraries - UCL Geography, University of London
  Library in Senate House, and British Library
• Stanfords map shop, Long Acre, Covent Garden,
  www.stanfords.co.uk
• Oddens map list, http//oddens.geog.uu.nl/

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www.lib.utexas.edu/maps.index.html
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Graphicacy

• literacy, numeracy and articulacy
• argued in modern world of screens and
  interfaces, that graphicacy is becoming more
  important
• understanding maps need graphicacy
• graphicacy skills of map-makers and map-users
• said to be inherent skill, but some are better
  than others. artistic flair, designer eye for
  form and layout
• everyone is potentially a map-maker. cant rely
  on the skills of professional cartographers

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How maps work?

• abstractions to make a scale model of reality
• c.f. famous fictional stories of the 11 maps
  selection
• 1. classification (grouping similar features) to
  reduce complexity and organise information
• 2. simplification
• 3. symbolization
• these are design processes (and are inherently
  subjective)
• there is no one true map of a phenomena or place

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Design

• there are some (scientific) rules in map design
• but much artistic judgement in terms of
• selection of colours
• symbology
• labelling (format and position)
• arrangement of overall layout
• (plus data selection, projection, scale, etc)
• subtle changes in design (e.g. weight of a label
  font for particular objects) can yield big
  changes in how the map is read
• use (and mis-use) the power of design. ethical
  practices not to deliberately deceive

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Design and dangers of defaults

• modern gis, mapping, drawing, DTP software is
  very flexible and powerful
• but still constrains design
• always question software defaults settings

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Tuftes principles of graphical excellence

• show the data
• induce the reader to think about the substance
  rather than the methodology, graphic design,
  gee-whiz technology
• avoid distorting what the data have to say
• present many numbers in a small space
• make large datasets coherent
• encourage the eye to compare different pieces of
  data

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Tuftes principles of graphical excellence

• reveal the data at several levels of detail, from
  broad overview to the fine structure
• serve a reasonably clear purpose description,
  exploration, tabulation or decoration
• be closely integrated with the statistical and
  verbal descriptions of a dataset

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Try to cover the following

• assumption of maps made for presentation, they
  need to be usable for general audience
• map layout
• map scale and generalisation
• symbolisation and graphic variables
• choropleth mapping data classification
• colour
• labelling and typography

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Map layout

• for presentation maps, some conventions on what
  to include
• a title (or caption). clearly state what the map
  shows. plus relevant date of data, sources,
  missing values, author, contact info, etc
• a legend, so any reader can interpret the content
  of the map. meaning of all symbol and colours
• scale indication. translates distance on the map
  to distance on the ground
• orientation indication (the good old north arrow)
• borders and neatlines
• these conventions are widely broken!

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Balance and centre

• Visual impact of arrangement. harmonious
  arrangement around the optical centre
• concern for weight and direction of objects
  around the natural centre
• unbalanced composition look random and accidental

optical centre
geometric centre
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Golden proportions
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1.618
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Interesting balance
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Map scale

• what level of detail is shown
• crucial to choose appropriate scale to work at
• large scale map small surface area in high
  detail (e.g. city plans)
• small scale large surface area in low detail
  (e.g. national road atlas)
• scale represented as a statement (one inch
  equals five miles), a graphical scale bar,
  (useful for measuring lengths), or as a
  representative fraction (11250)
• very few maps use scale consistently for every
  object

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Key modes of generalisation

• distortion is inherent,
• inevitable, unavoidable
• may have to leave
• features off the map
• altogether
• avoid visual clutter,
• balance content and
• legibility

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Map symbolisation

• graphic language (of points, lines, polygon,
  icons and text) used to represent real features
  on the map
• legibility (practical)
• harmonious (pretty)
• symbols can be iconic, geometric or abstract
• symbol selection is creative aspect of design,
  wide choice and few firm rules
• symbols can have several different dimensions
  (properties or characteristics) which encode
  meaning
• symbols can have quantitative or qualitative
  meaning

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Graphic variables for symbols

• shape, size, orientation
• colour hue, colour value, colour saturation,
  pattern
• and location of course

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(Source Larry Landweber, http//www.cs.wisc.edu/
lhl/maps/)
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Choropleth maps

• counterpart of histogram
• aggregate data, usually ratio or percentage
• data map for discrete spatial units
• choro from choros (place) and pleth (value)
• practical Issues
• choice of intervals - number and their breaks
• equal interval, equal share (quantiles), standard
  deviational,
• choice of colors
• important for perception of patterns
• misleading role of area of spatial units
• larger areas seem more important

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• very widely used. the default mapping,
  especially for social data (e.g. census)
• most mapping tools produce choropleth maps
• easy produced in GIS, stats software
• not necessarily the best solution
• problems. can easily promote false notions of
  homogeneity inside the zones and sharp cut-off at
  the borders. real phenomena (e.g. Internet
  access) do not fit neat set of units
• should be used for ratio data and not absolute
  counts as most spatial units are variable in size

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Data classification

• classification is a key method of abstracting
  reality into simplified map
• method of classification is important as effects
  look of the map
• classification scheme can easily be experimented
  with (manipulated?) to give the pattern you want
• classification should match data distribution
• number of classes. can reader interpret between
  them? recommended max of 6
• distribution of zones into classes

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Same data plus different classification equal
different looking choropleth map!
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Classification options from ArcMap

• natural breaks (Jenks method),
• quantiles,
• equal interval,
• standard deviation
• See handout from Dent (1999, page 145)

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• Technical reading
• Evans, (1977) The selection of class intervals,
  Transactions of the Institute of British
  Geographers, 53, pp. 98-124. (available from
  JSTOR)
• Jenks and Caspall, (1971) Error on choropleth
  maps Definition, measurement and reduction,
  Annals of the Association of American
  Geographers, 61, pp. 217-244. (available from
  JSTOR)
• Miller (1956) The magical number seven plus, or
  minus two some limits on our capacity for
  processing information The Psychological Review,
  63, pp. 81-97. (www.well.com/user/smalin/miller.ht
  ml)

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The role of colour

• colour is one of most exciting aspects of design
• colour perception is a combination of
  physiological (sensing in the eye and cognitive
  processing) and psychological reactions
• colour evoke emotions. subjective reaction to
  colour
• connotative meanings of colour. See Dent (1999,
  page 295)

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Defining colour

• cultural specific. also colour blindness. 7 of
  men and 1 of women
• warm colours (red, orange, yellows)
• cool colours (violet, blue, greens
• defining - hue, saturation, value (HSV) model

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hue - basic colour we perceive, eg 12
step wheel value - lightness or darkness. Can be
hard to perceive variations in value saturation
- intensity or purity compared to a neutral gray
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Design and colour

• gives structure and readability
• developing figure and ground relationships
• warm colour better for figures. Said to advance
  to viewer. Cool colours tend to recede
• perceptual grouping of like features through
  colour
• colour contrasts. using value or saturation to
  represent data on thematic maps
• qualitative conventions - blue for water, green
  for lush vegetation red warm and blue cool
  in temperatures hill shading

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Labelling the map

• lettering choice can have a significant impact to
  effectiveness of the map
• typography - practical and personality
• map text to label features has several key
  parameters
• font typeface, size spacing
• placement and orientation
• importance of type discernibility
• map labels can communicate important data, e.g.
  hierarchy of features, implying importance
• Chislehurst, Bromley, L O N D O N
• manual labelling of features can get very
  tedious. but automatic label placement is still
  far from perfect

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Think about different types of lettering styles
and placement/orientations used and the effects
it has
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Some considerations

• from Dent (1999, page 271)
• legibility of individual letters is of paramount
  importance, especially in smaller type sizes.
  Choose a typeface in where there is little chance
  of confusion between c and e and i and j
• select a typeface with a relatively large base
  height
• avoid extremely bold forms
• choose a typeface that has softer shading
  extreme vertical shading is more difficult to
  read than rounder forms
• do not use decorative typefaces on the map as
  they are difficult to read

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Code of ethics

• for thematic map cartographers, from Dent (1999,
  page 19)
• 1. always have a straightforward agenda, and have
  a defining purpose or goal for each map
• 2. always strive to know your audience, the
  potential/likely map users
• 3. do not intentionally lie with data
• 4. always show relevant data whenever possible
• 5. data should not be discarded simply because
  they are contrary to the position held by the
  cartographer
• 6. at a given scale, strive for an accurate
  portrayal of the data

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Code of ethics

• 7. the cartographer should avoid plagiarizing
  report all data sources
• 8. symbolization should not be selected to bias
  the interpretation of the map
• 9. the mapped result should be able to be
  repeated by other cartographers
• 10. attention should be given to differing
  cultural values and principles

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Further reading

• Borden Dent, (1995) Cartography Thematic Map
  Design, fifth edition
• Terry Slocum, (1999) Thematic Cartography and
  Visualization
• Menno-Jan Kraak and Ferjan Ormeling, (1996)
  Cartography Visualization of Spatial Data