Color Enhanced Maps

  • Topics
  • Scientific Visualization Objectives
  • Earth and Environmental Science Objectives
  • Tools
  • Teacher Instructions
  • Text References
  •  Student Assignment
  • Evaluation Criteria
  • Purpose:  To explore and apply concepts of visual perception and the properties of color.
    Overview:  Students will download or create maps with numerical weather data.  They will add isolines (contour lines) and color to create regions on their maps.  They will then explore the visual properties of various color palettes and discuss the advantages and disadvantages of various color coding schemes. They then create a visualization applying their knowledge of color properties.
    Topics:

        Scientific Visualization:  Color Properties
        Science: Earth and Environmental Science

    NC Scientific and Technical Visualization Objectives:

      Level I:  4.03C  Identify color properties
                          G  Identify and apply guidelines for the effective use of visual properties to code visualization variables.
      Level II: 2.01B  Advanced color usage
                    2.01C4b Isoline graphs
                   3.01C  Identify and apply color lookup table techniques.
                   3.02     Apply advanced area rendering techniques

    NC Earth and Environmental Science Goals and Objectives (objectives from 1994 revision):

    Goal 6:    The learner will have an understanding of location and mapping.
    6.1.1       Through  activities, recognize the types of information provided by different  kinds of maps and the methods used in their construction.
     

    Tools

    Scion Image
    NIH Image
    CorelDraw
    Teacher Instructions

    Color is a valuable tool in creating a scientific visualization.  Beyond making a visualization more attractive, color can be used to encode data, elucidate patterns, and draw the viewers attention to important details.  In order to choose the color scheme for a visualization the perceptual properties of colors and the anticipated output medium must be considered.  In this exercise students will work with different color schemes to explore their  perceptual properties. They will participate in discussion,  create isolines  and  color coding for given maps, and answer discussion questions.  Suggestions for a final project which may also be assigned are included.  Students  should be encouraged to use the correct technical terms which are outlined in the  key  vocabulary section below  in discussion.  The teacher may choose to include a more technical discussion of the electromagnetic spectrum and the wavelength of light.  This could be related to objectives in Physics and  Physical Science.

    DISCUSSION OUTLINE
    This activity requires the use of isolines which students may be more familiar with as contour lines if they have ever worked with a topographic map.  If they are not familiar with topographic maps they should see one, preferably of their home area.  They can also visit http://mapping.usgs.gov/mac/isb/pubs/booklets/topo/topo.html which is an excellent discussion from the  USGS (United States Geological Survey) on topographic maps.

    Begin a class discussion of color coding in maps by viewing  a selection of  maps from various sources - newspaper weather maps, census maps, historical maps etc. are a good place to start  work but if possible have students find internet examples of different types of color coding.    Discuss the use of color to code for data.   What color schemes are familiar?  ( For example, the use of darker colors to represent more and the use of reds to represent warmer temperatures.)   What issues do we have to be careful of when using color coding?  (Colors that are too close for people to perceive the difference,  distracting people from the information, needs related to the output medium.) What types of data are best coded by hue shifts? lightness and saturation shifts?  (Hue often indicates qualitative data such as vegetation type, lightness and saturation signal quantitative shifts.)

     Below are some internet examples from February 1999.  Of course these should be checked before the lesson as internet material is subject to change.  Most of these maps use combinations of all three perceptual properties of color.  After discussing some of the maps as a class ask students to work independently or in small groups to analyze and discuss the use of color in a selection of other maps.

    Maps where hue is used:
    http://edcintl.cr.usgs.gov/adds/c1/doc/demd/c1demd.gif    This map of  Africa uses mostly hue but also saturation for elevation.  Elevation,  which is quantitative variable,  could also be shown effectively  with lightness and saturation but color is more vivid and indicates the qualitative differences in the ecology of these regions at the same time.

    Maps where lightness is used:
    satellite weather image from Feb. 12, 1999   or check for today's image at   http://iwin.nws.noaa.gov/iwin/nc/nc.html      These images use gray scale which can be thought of as completely desaturated with no hue. Changes in lightness are also referred to as changes in value or brightness.  Gray scale must be used when there is a possibility of a black and white output medium (most printers in schools).  Gray scale in combination with one color (red) in density slicing where areas with a particular value can be highlighted.

    Maps where both are used:

    http://www.botanik.uni-bonn.de/biodiv/phytodiv.htm     This map uses an effective combination of hue and saturation.  The saturation shift shows the quantitatively greater number of species in the highly saturated areas which are also for the most part small  in area so that the high saturation emphasizes these areas without being overwhelming.   The hue shift helps the viewer perceive the differences.

    http://www.wcmc.org.uk/forest/data/wfm.htm   This map uses hue and saturation ineffectively.  The colors used for tropical dry and for mangrove are difficult to distinguish from other colors and the saturation shift is being used inappropriately for a qualitative variable.

    North Carolina Temperature Anomaly Map - used with permission from the State Climate office of North Carolina     This map shows how temperature patterns in North Carolina differed from normal in 1997.  It is an interesting color coding example because it uses one hue, blue, to code for negative differences from average  and other hues, green and yellow to code for positive differences.  Lightness is used to code for the amount of the difference in the blues.

    http://nic.fb4.noaa.gov/products/analysis_monitoring/enso_advisory/advfig1.gif     These two sea surface temperature maps are good choices for student analysis.
     
     

    MAP ACTIVITY

    Now students should take a map with numerical data and use color to code it.  They may start with the linked map below or use another map that allows the same type of exercise.   Click here to get a downloadable tiff file which can be opened in Scion Image:  North Carolina Temperature Map


     

    Some possible map assignments are listed below.  More group assignments can be developed as necessary by mixing  different temperature ranges with different color coding schemes.  You  could assign all students to produce all maps but that is not necessary for the lesson.  Each working group of students can produce 2 or 3 maps and then all of the maps should be posted or projected for discussion.  Each group should produce at least one map where lightness alone is used to code and should produce maps with two different  widths of temperature ranges.  Students will follow directions on the student assignment sheet to create a custom LUT (color lookup table).

    Group 1:
    map 1:
    2º temp ranges,    uses hue changes only,  keep lightness and saturation constant.
    48-49
    50-51
    52-53
    54-55
    56-57
    58-59
    60-61:
     

    map 2:  5º  degree temperature ranges, red map: use lightness changes only.
    45-49
    50-54
    55-59
    60-64
     

    Group 2:

    map 1:  2º temp ranges, blue map: change lightness and saturation.
    48-49
    50-51
    52-53
    54-55
    56-57
    58-59
    60-61

    map 2:  5º  temp ranges, yellow map:  use lightness changes only.
    45-49
    50-54
    55-59
    60-64
     

    Students should begin by finding  and drawing lines around  regions that are in the same temperature range.   They need to be sure each region is completely enclosed, otherwise the paint bucket tool will spill the color into the next region.  Then they use the paint bucket to fill each region with a different color according to their assignment.   Finally  they will develop a legend and present their map to the class - either printed on a color printer or on screen.    After viewing and discussing all of the maps students should answer the discussion questions.

    Here is an example of the type of map students should be producing:  This map uses only lightness - hue (Blue = 160) and saturation (full = 240) remain the same.  The temperature range width is five degrees so only four color codes are needed.

    A possible extension is to ask students to produce a color coded map of their choice and write a brief reflection on why the color coding scheme they chose is appropriate for their data.  Students can scan in or find on the internet the base map they use for their project but the color coding scheme should be their own.

    Possible ideas for student maps:

    North Carolina Rainfall:  data is not neatly summarized anywhere.   http://iwin.nws.noaa.gov/iwin/nc/nc.html is a site with links to a lot of North Carolina weather information.  An hourly summary of temperature etc is available at:  http://iwin.nws.noaa.gov/iwin/nc/hourly.html   while .http://iwin.nws.noaa.gov/iwin/nc/climate.html    has daily summaries and a variety of other info (sunrise and set times, record for the day, mean monthly temps etc).  A site with links to   http://www.nc-climate.ncsu.edu/

    Range and population estimates for different species of animal (e.g. mountain lions, grizzly bears).  Students could produce a map showing where various species are found, investigate the habitat of the various species, do population density maps etc.  Data, particularly for the endangered and charismatic megafauna (like wolves, bears, and whales) is  available at many sites.  This is also good web search project.  For example bear data can be found at:   http://www.bearden.org/species.html

    Census Topics - this can combine social studies and science:  data available at:   http://www.census.gov/

    Epidemiology of various diseases:  http://www.epibiostat.ucsf.edu/epidem/epidem.html

    A color coded  map of your school.

    Human Anatomy:  data available at:  http://www.nlm.nih.gov/research/visible/
     

    Key Vocabulary:  Students will explore the meanings of these key terms during the lesson.  Definitions should not be given out as notes, however they should  be used correctly in the discussion of the maps as a part of the conclusion of the lesson.

    color:  The quality of a surface which results from a response to lightness, hue, and value.  Hue is often confused with color since the names of the hues are used as the primary classification  term for color. (e.g. red, purple, blue, etc.)

    color lookup table (LUT)  A database which allows colors to be mapped to specific data values.  A color table can be associated with a single image or used as a standard table in a library.

    hue:  the controlling spectral wavelength of the perceived color.  Hue and color are often confused because the name given the hue is often synonymous with the color.

    saturation:  A perceptual color quality indicating the ratio of the primary spectral wavelength (hue) to all the wavelengths in the color.  A high saturation color appears vivid whereas a low saturation color appears grayish.

    value (lightness, brightness)  A quality of color indicating the total quantity of light energy.  On a gray scale the lightest color, pure white, has the highest quantity of light.

    isolines:  often called contour lines, are used in mapping quantitative data such as temperature or altitude.  All of the values along an isoline are equal.

     


    Text Reference

    Bertoline, G.R.,  Wiebe, E.N., Miller, C., & Mohler,J.L. (1997) Technical Graphics Communications. (2nd Edition). Burr Ridge; IL:WCB/McGraw Hill color: p995-998, contour plots, isolines: 948-950, choosing colors: 958-961, perceptual accuracy p. 963-964.



    Student Assignment Sheet                                                                        Name______________________

    Purpose:  To create and compare maps with a variety of color coding schemes.

    1.  Open the North Carolina Temperature map in Scion Image (or another image processing software).

    2.  Save a copy of your map with a different name.

    3.  Draw isolines for the regions assigned.

    4.  Magnify your map to be sure that each region is completely closed.  Add lines to close the regions where needed.

    5.  Choose colors according to your assignment.  In order to manipulate the hue lightness and saturation separately you will have to custom create a LUT.   In Scion Image choosing  the eight grays LUT and changing some of the grays to custom colors  is a good way to start.    You can do this in Scion Image by first going into color tables on the options menu and selecting 8 grays, then select the color picker tool (that's the one that looks like an eye dropper) and then double click on the LUT region that you want to choose a new color for.  The color palette dialog box will pop up and  allow you to experiment with changing the hue, saturation and light separately either by moving the cursor within the color box or by separately adjusting the numerical value for each of these color factors..  You can't pick all eight colors at once - you must click on the color picker and then double click on  a new region of the LUT and go back to the palette dialog each time you want to add a color to the LUT.

    6.  Once you have a LUT that fills the requirements of your assignment use the paint bucket to fill the different temperature regions.  If the paint spills out of the desired area you have a hole in the lines enclosing a region.  To fix the problem  you must use undo (under the edit menu) before doing anything else or else revert to saved.  Then magnify your image, find the hole and draw a line to close it.

    7.  Set up a temperature color legend.

    8.  Produce other assigned maps according to the same steps.

    9.  After looking at and discussing all of the maps answer the worksheet questions.

    10. Choose a topic which will illustrate the use of color coding in mapping, define a purpose for and produce a final map.  Your map should illustrate excellent use of color coding.  Keep in mind that the choice of color scheme depends on the output medium assigned.

    11.  Write a brief reflection on why the color scheme you chose is most appropriate for this map.
     

    Questions:

    1.  From your observations of the maps produced by the class which hue has the greatest perceived lightness range?  The smallest?

    2.  The U.S. temperature forecast map in most newspapers gives a different color code for each 10 degree change in temperature.

        a) Would this be appropriate to show the temperatures on the North Carolina map in this exercise?  Why or why not?

        b)  What advantages and disadvantages does the 10 degree range have for the US temperature map?

    (Eric you suggested "Is this color increment appropriate for the US map -since it is widely used I would assume and so will the students that the answer is yes - what I want to draw out is that a 10 degree increment on a small scale map leaves out a lot of local detail (like elevation related changes in the Rockies) but gives a clear overall picture.)

    3.  Discuss the advantages and disadvantages of using a narrower range of temperature for each color code.   What does using a narrow range and a lightness shift imply to the viewer - perception compared to a  larger range and a hue shift. What width of temperature range do you think is most appropriate for the map used in this exercise?
     

    4.   A meteorologist decides to make it easier for people to see the boundaries between regions by  alternating light and dark in her temperature scale.  The scale looked like this:
    90-100 very dark red
    80 - 90 light red
    70 - 80 dark red
    60 - 70  medium red
    50 - 60 white

    What is wrong with a scale like this for a temperature map?

    5.  What is a color lookup table?
     

    6.  In what situations is it better to use a gray scale?

    7.  Precipitation maps often use lightness or saturation for coding while vegetation maps usually use hue or a combination of hue and lightness or saturation.

    a.  Why is this?

    b.  What would be best for coding population density?

    c.  What would be best for coding  a world map showing the language spoken by the majority population in each region or country?

    d.  What would be best for coding region's mineral resources (keep in mind that some regions may have several minerals while others have none)?

    8.  When you plan a project you need to know what type of output medium you will be using.  Write how planning will be affected by each of the following output devices:

    color laser printer

    color bubble jet printer

    laser printer

    web page

    web page to be projected in a classroom using a LCD projector

    web page to be broadcast on TV
     
     
     
     
     



    Evaluation Criteria:
    A possible division of points is listed below:

    Success will be measured by the following criteria:
    Produces assigned maps:
      5    draws isolines
      5    shades regions
    10    demonstrates ability to keep hue and saturation constant while changing lightness
      5    saves map
      5    prints or presents map

    35   Answers questions

    Final project map
    10   Produces student  map
    10   good use of color for chosen data
    15   paragraph on why color choice is appropriate

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