Geography 222 The Power of Maps

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Geog 222 Lecture Outline: Map Abstraction
Update: 3/30/14

Map Abstraction


1. Map Content: given the infinite detail in the physical and human environment, what is selected to be mapped?

2. Map Scale: "the extent of size reduction from the environment to the map; the ratio of map distance to ground distance"

3. Map Generalization: the systematic process of removing detail from (and sometimes adding detail to) the objects and phenomena to be mapped

4. Map Symbolization: the systematic process of creating graphic marks which represent the objects and phenomena to be mapped



1. Map Content: given the infinite detail in the physical and human environment, what is selected to be mapped?

Two basic types of cartographic maps: reference vs thematic

Further distinctions: variations in map content...where, when, and what


What gets selected to get mapped is a function of the purpose of the map and the available data.

PDF) Review Making Maps ch 2 pp. 27-31, 32-33


Map Vantage Point, Vertical Viewing Angle, and Perspective

Vantage point: the position that the map maker takes with respect to the earth's surface




Vertical viewing angle: view from above (plan) or the side (oblique)




Perspective: how we see (rather than from where)




2. Map Scale: "the extent of size reduction from the environment to the map; the ratio of map distance to ground distance"


PDF) Making Maps ch 5 pp. 110-111


Map Scale Types


Relationship between scale and what is shown on a map (generalization) and how things are shown (symbolization): on paper and digital maps:




3. Map Generalization: the systematic process of removing detail from (and sometimes adding detail to) the objects and phenomena to be mapped

Monmonier: "A map that did not generalize would be useless"


3a. Selection


First step in the generalization process, driven by the purpose of the map:




3b. Simplification and Smoothing

The systematic process of removing detail and angularity from the objects and phenomena to be mapped


Simplification: removing detail from a particular feature


Smoothing: changing the location of some of the points and adding new points to make the line look smoother


3c. Displacement

Moving features on the map apart so that they do not interfere with each other




3d. Enhancement

The systematic enhancement of objects and phenomena to be mapped


3e. Dimension Conversion

Generalizing from one dimension (point, line, area) into another




3f. Data Classification:

We classify qualitative data as part of the map generalization process


We classify quantitative data as part of the map generalization process


PDF) Making Maps ch 8 pp. 170


"Classification reflects the point of view taken by those gathering data and making maps more than it does inherent phenomenal traits. There are no classes in reality; classes are the product of human cognition."

Two basic elements of classification: number of classes and class breaks


Number of Classes

How much do we aggregate our data together?

Qualitative data classification




Quantitative data classification




Class Breaks (or limits)

Given a set number of classes (5, 6, 7, etc.), where do you place breaks between the classes?


PDF) Making Maps ch 8 pp. 180


Qualitative (nominal) geographic data



Quantitative (ordinal, interval, ratio) data it is a bit more complicated




Common Class Break Schemes

Equal (or constant) interval



Quantiles



Important: You will see different patterns depending on how the quantitative data on a map has been divided up


PDF) Making Maps ch 8 pp. 182-187




Data Classification and the 2010 U.S. Census Data

1. Go to this data table of selected social characteristics (by U.S. State)

2. Click on Back to Search tab.

3. Click on Geographies button (to the left).

4. Click on All States within the United States in the list under Geography Name.

5. Close the Geographies window (hit X in the upper right corner of the pop up window).

6. Click on SELECTED SOCIAL CHARACTERISTICS IN THE UNITED STATES (DP 02, second in list).

7. Click on Create a Map

8. Scroll down and click on a row of data you are interested in seeing mapped (click on the first number in the row)

9. Hit Show Map on pop-up window.

10. Click on Colors and Data Classes. You can change the number of classes (5 is default) and the classification scheme (four options)

11. Using the same data set (row):

12. Using the same data set (row):

13. Place your five JPG maps into a Word or Open Office document. Compare the two maps with 3 and 7 classes, as well as the three maps with three different classification methods. Jot down some notes about the differences you see, and email me the document.




4. Map Symbolization

Vital, final step in the map abstraction process

Symbol: A thing representing something else because of relationship, association, convention, or resemblance.

Map symbolization: the systematic process of creating graphic marks which represent the objects and phenomena to be mapped



PDF) Making Maps ch 9 pp. 196


4. Cartographic Design Structures: Visual Variables

How do you logically link data to graphic marks on the map?


4a. The visual variables



4b. How to use the visual variables as a guide to design and symbolization



4c. A few Important Visual Variables Described and Illustrated


  • Size: changes in size imply a quantitative difference




  • Shape: changes in shape imply a qualitative difference




  • Color Value: value is the variation in lightness or darkness of a color and implies quantitative difference; usually light means less and dark means more




  • Color Hue: usually what people associate with the word "color," hue implies a qualitative difference







    Visual Variables can be used together:



    Sum: Map Abstraction and Infrastructure

    Map (or cartographic) Abstraction: "the process of transforming geographic data, which represents the actual human and physical environment, into a map

    All vital steps in transforming geographic data into a visual representation of that geographic data: a map


    1. Map Content: given the infinite detail in the physical and human environment, what is selected to be mapped and at what scale?

    2. Map Scale: "the extent of size reduction from the environment to the map; the ratio of map distance to ground distance"

    3. Map Generalization: the systematic process of removing detail from (and sometimes adding detail to) the objects and phenomena to be mapped

    4. Map Symbolization: the systematic process of creating graphic marks which represent the objects and phenomena to be mapped




    E-mail: jbkrygier@owu.edu

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