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Evaluating Cartogram Effectiveness

Presenter: Chun-Hung YuDate: Wed , Aug 11, 2020
Publisher: IEEE Transactions on Visualization and Computer GraphicsPublished in: Feb 1, 2018, Volume: 24 , Issue: 2

Abstract

  • The large number of cartogram types, there are few studies evaluating the effectiveness of cartograms in conveying information.
  • Four major types of cartograms
    • contiguous cartograms
    • non-contiguous cartograms
    • rectangular cartograms
    • Dorling cartograms (i.e circular)

Four major types of cartograms

Contiguous Non-contiguous Rectangular Dorling

Step

  1. We first evaluate the effectiveness of these cartogram types by quantitative performance analysis (time and error).

    • 7 visualization tasks in cartograms

  2. We collect qualitative data with an attitude study and by analyzing subjective preferences.

  3. We compare the quantitative and qualitative results with the results of a metrics-based cartogram evaluation.

  4. We analyze the results of our study in the context of cartography, geography, visual perception, and demography.

  5. We consider implications for design and possible improvements.

Cartogram Types

  • 3 major design dimensions
    • Statistical accuracy : 面積
    • Geographical accuracy : 形狀
    • Topological accuracy : 相鄰關係

Contiguous Cartograms (also called deformation cartograms)

  • Deform the regions of a map by pulling, pushing, and stretching the boundaries.
  • Allow for some cartographic error in order to better preserve shape and topology.

Rectangular Cartograms

  • In rectangular cartograms there is often a tradeoff between achieving zero (or small) cartographic error and preserving the map properties (relative position of the regions, adjacencies between them)

Non-contiguous Cartograms

  • They satisfy area and shape constraints, but do not preserve the topology of the original map.

Dorling Cartograms

  • Data values are realized by size of the circle. However, in order to avoid overlaps, circles might need to be moved (typically as little as possible) away from their original geographic locations.
  • Unlike contiguous and noncontiguous cartograms, Dorling cartograms preserve neither shape nor topology.

7 Visualization Task In Cartograms

  • Cartograms two type of information: geographical and statistical.
  1. Compare
  2. Detect Change
  3. Locate
  4. Recognize
  5. Find Top-k
  6. Find Adjacency
  7. Summarize

1. Compare

For similarities or differences between attributes.

2. Detect Change

Whether a region has grown or shrunk is a central feature, it is crucial that the viewer be able to detect such change.

3. Locate

Fnding the position of a region in the cartogram.

4. Recognize

The viewer can recognize the shape of a region from the original map when looking at the cartogram.

5. Find top-k

Find out the region with the highest or second highest value of an attribute.

6. Find Adjacency

To identify the neighboring regions of a given region.

7. Summarize

To convey the “big picture”.
Summarize tasks ask the viewer to find patterns and trends in the cartogram.

Attitude Study

Discussion

So, Which Cartogram is Best?

Design Implication

可以使用一些交互技術來彌補每種製圖的缺陷，像是滑鼠 hover 顯示資料資訊或者工具提示標籤等等…

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