1. The Cartogram: Value-By-Area Mapping SP 240 Cartography Alex Chaucer

2. Spatial Information Technology Center The Value-By-Area Cartogram Defined Cartograms, or value by area maps the area of internal enumeration units are proportional to the data that they represent. No data is lost; data represented as area.

3. Spatial Information Technology Center Brief History of the Method 1868/1875 Levasseur 1963 Tobler stated “maps without projection system” see in atlases and general reference books

4. Spatial Information Technology Center Two Basic Forms Emerge Contiguous Cartograms Internal enumeration districts are adjacent to eachother Easier to see the entire area NonContiguous Cartograms Does not preserve boundary relations Easier to compare and scale, can maintain true shape

5. Spatial Information Technology Center Mapping Requirements Can learn the shape of countries, counties Cartograms offer a unique view of geographical space Shape quality – if shape is important, don’t use the cartogram Size will be transformed, while keeping other aspects Reader should be able to recognize shape Strive to maintain orientation

6. Spatial Information Technology Center Communicating With Cartograms Success with cartograms is not always guaranteed There are three potential problem areas 1. Shape recognition 2. Estimation of area magnitude 3. Stored images of the map reader

7. Spatial Information Technology Center Recognizing Shapes Shape is how we recognize objects Can draw points to create a straight line generalization (11.7)

8. Spatial Information Technology Center Estimating Areas Distortions can interfere with area estimations Irregular polygons work best Legend should represent low, mid, and high end of the data range

9. Spatial Information Technology Center A Communication Model Shape should be maintained A geographic inset map should be included in case the map reader is unfamiliar with the area Well-designed legend

10. Spatial Information Technology Center Advantages Are innovative and interesting Communicate some spatial information Present a generalized reality Thought-provoking May shock the reader Have some clarity See distributions in new ways

11. Spatial Information Technology Center Disadvantages “inaccurate” base map Readers may be confused by the logic of the method Specific locations may be difficult to identify due to distortion Have not been tested enough to totally understand how map readers react to them

12. Spatial Information Technology Center Two-Variable Cartograms May give a new perspective May be some compatible methods for two-variable representation Can use graduated color or graduated point symbols within each enumeration district

13. Spatial Information Technology Center Cartogram Construction There are two ways to produce value-by- area cartograms 1. Manually 2. Computer Technology

14. Spatial Information Technology Center Manual Methods Divide total population (or whatever to be mapped) by number of square inch units This will give you counting units These counting units will then be arranged in the shape of the original enumeration district Each states shape is adjusted until the cartogram is completed Space with zero values should at least be listed on the map as having zero values Constructing a non-contiguous cartogram is different; retains the shape of each state

15. Spatial Information Technology Center Computer Solutions There are computer programs available Can take many forms Can reduce time and “drudgery” of production, but should not interfere with the designer’s choice

16. Spatial Information Technology Center Demos http://www.mapresso.com/dorling/dorling.html http://www-personal.umich.edu/~mejn/election/ http://www.jatrigis.com/cartogram/cartogram.htm