I appreciate all the feedback I’ve got in emails, on this blog and on other blogs. Especially, I’m thankful for critical feedback as this is helping me in addressing important issues. Most of the critical comments are questioning the effectiveness of 3d globe visualisations, which are widely used on this blog.
We definitely need to think critically about the pros and cons of 3D visualisations. I want to give my response in a series of blog posts.
Rich Treves made a comment where he linked to his blog post “3D Rears its Ugly Head Again”. This is the first of his three arguments against 3D KML (Rich, excuse me for taking your arguments out of context!):
“I can't compare the Oil consumption of UK and Australia at the same time because they are on different sides of the globe.”
True, the ability to compare all countries is lost when thematic maps are rendered on a globe. Still there are various ways to address this issue:
1. I’m using two visual variables (colour and height) to represent the same statistical indicator. This makes country comparison easier when spinning the globe.
I could not find oil consumption statistics at UNdata, so I'm using "Infant Mortality Rate" instead (per 1,000 live births). You can make the map in the Thematic Mapping Engine, or download the KMZ file here. I think this is a good and effective 3D visualisation.
2. Values can be displayed on the globe, which makes country comparisons much more accurate.
I added this feature to the Thematic Mapping Engine yesterday. More info will come in a separate blog post.
3. Another option, which is now possible with the new Google Earth plugin, is to have two spinning globes in the same window.
Click here for a live example (based on the China Syndrome example from Google Code). If you rotate the left globe, the right globe will show you the view on the other side. I think it would be better to enable the user to rotate the two globes indepentantly.
4. A different approach is leave the globe, but hold on to 3D KML using a tool like UUorld, where you have 3D prisms on a flat world map.
Currently, there are no 3D KML renderers that are able to make such visualisations, but I’m sure there will be in the near future. Maybe a job for the UUorld guys? UUorld seems to use Plate Carrée (Equidistant cylindrical) projection. This is clearly not the best choice for thematic world maps, but it’s the same projection currently supported by KML (EPSG:4326).
In conclusion, country comparisons are problematic on a 3D globe, but it shouldn’t stop us from doing it!