Textbook: Slocum, T.
A. 1999. Thematic Cartography
and Visualization. Prentice Hall: New Jesey.
URL :
https://www.angelfire.com/mo/yagoub
Chapter 6: Color
Schemes for Uni-variate Choropleth and Isarithmic Maps
See Page:
105-116
What is an appropriate color for
Uni-variate Choropleth and Isarithmic Maps? Shall I use lightness of a single
hue (e.g. green) or a combined hue-lightness scheme (e.g. bright yellow to dark
red)?
Why is the focus on color for
Uni-variate choropleth and Isarithmic maps?
Because of their common use
List
the main factors for selecting an appropriate color scheme?
1.
Map use task
Map use refers to whether the map is
used to obtain specific or general information. Unordered hue-based schemes
(Plate 6.1 A) worked best for acquiring specific information. While ordered
lightness-based (Plate 6.2 A) and combined hue-lightness (Plate 6.1 E, and F)
schemes worked best for acquiring
general information.
2. Kind of data
Kind of data refers to the three
kinds of numerical data: bipolar, balanced, and unipolar. Bipolar data
have either natural or meaningful dividing points: for example, percentage of
population change has a natural dividing point of zero. For bipolar, diverging
schemes is recommended, in which two hues diverge away from a common light hue
(Plate 6.1 B) or a neutral gray. Balanced data are characterized by two
phenomena that coexist in a complementary fashion: for example, the percentage
of English and French spoken in Canada, the percentage of citizens and
expatriates in the UAE. For balanced data, diverging scheme is recommended to
emphasize the mid point of the balanced data (Plate 6.1 B). Unipolar
data have no dividing points and do not involve two complementary
phenomena. For unipolar, lightness
scheme is recommended (Plate 6.2 A).
3.
Type of map
Types of map refers to the general
method of symbolization used (Choropleth or Isarithmic). Spectral color scheme
(Plate 6.1 C) can be used on isarithmic maps if the colors are shown in
association with contours and/or hill shading (long-wave colors such as red
appear closer to the viewer than short-wavelength colors such as blue).
List other
factors for selecting an appropriate color scheme?
Additional
factors in selecting color schemes include (page 108-111):
1. Color association (e.g blue for
water, green for vegetation)
2. aesthetics (e.g. preference of some
cultures to blue over yellow-orange-red)
3. Color vision impairment (people
who can not distinguish red from green)
4. Age of the intended audience
(children, adults: e.g. adults understand the blue-to- red scheme commonly used
for representing
temperature data)
5. Whether the map is intended for
presentation or data exploration
6. Economic limitation (e.g. cost of
hardware, software, and color maps in books)
7.
Client requirements (mapmaker sometimes have to respond to client requirements)
