This was part of a talk I gave at a geospatial workshop at Oxford. My focus was on the issue of mixing together different types of data with differing spatial frequencies. This line of thinking eventually led to the paper "Visual Multiplexing".

1. Multiplex encoding in
multi-layer
visualisations
Simon Walton, Oxford e-Research Centre

2. Overview
• Multilayer visualisations; emphasis on
cartography
• Multiplexing as a possible solution

3. Map Overlays
Charles Booth John Snow

4. Map Overlays
- McHarg (1971)
“...let us map physiographic
factors so that the darker the
tone, the greater the cost. Let
us similarly map social values so
that the darker the tone, the
higher the value. Let us make
the maps transparent.When
these are superimposed, the
least-social-cost areas are
revealed by the lightest tone.”

7. The Role ofVisual
Perception
• Most cartographic works use ‘perception’
with more emphasis on aesthetic
qualities rather than visual understanding
• Who is the target of the visualisation?
• Public visual communication; vs
• Private visual thinking

9. Using spatial frequency

10. Dali

15. Conclusion
• Layered visualisations largely an unsolved
problem
• A layered visualisation can be
`modulated’ to assist user’s visual
decomposition of each layer
• Not enough emphasis on visual
perception theory in cartography / GIS