Friday, April 24, 2009

Axis on 3D Thematic Maps

There is a history of me posting about the use of 3D thematic maps on this blog, latest entry which links back to others here. Mostly this is reaction to Bjorn's work . Mark of Axis Maps has recently joined the conversation with a detailed post claiming 3D thematic maps are chart junk.

Mostly I agree with Mark, he mentions a number of issues about the use of 3D thematic maps that I've already written about:
  1. You can't see all the countries on a virtual globe at once - a traditional projection maps is better
  2. The prism for once polygon can obscure another
  3. Values of 3D polygons are difficult to read off
he goes into considerable detail about exactly why point 3 is valid beyond what I've said.

A partial defense of 3D thematic maps: Since I first commented on the use of 3D in thematic maps I've warmed a little to to the idea. If you are dealing with a country that is able to be viewed all at once (like the UK) you could represent values for counties as fixed width columns. This would reduce the occlusion problem and would also stop people mixing up volume/height of the prism with the variable being displayed: its clearly related to height. As for reading off exact values, you can set up polygons on the ground which pop up a balloon with the value when rolled over with the mouse. Also, you could color the columns to relate to a color key which would allow quick 'actual value' reading without needing mouse movement. Having done some background reading on vision recently I suspect that this sort of display may be more memorable to non-expert map readers especially if there is some sort of large outlier value (e.g. if the variable is 'number of millionaires' in each county in the UK then there would be far more millionaires in greater London county than anywhere else).

Test it!: However, the above is only a suggestion, overall I agree with Mark that we have a workable system for displaying thematic maps now (2D color) and I whole heartedly endorse his point:
"...most importantly, do some user testing before presenting a new technique as the best thing ever: It’s how research works and why it is important."
That being said. I do think that he's missed a point with the title of his post:
"Virtual Globes are a seriously bad idea for thematic mapping"
and his last paragraph:
"So what things are Google Earth (and other Virtual Globes) good for? The consensus around here is (1) to engender, quite powerfully at times, a qualitative “sense of place” or “immersion”; (2) for virtual tourism (e.g., sit on top of Mt Everest) or virtual architecture/planning; and (3) to perform a kind of viewshed analysis and see what can and cannot be seen from locations (line-of-sight). All of those are inherently 3D-map reading tasks in which the immersive, 3D nature of the map is important. By comparison, population data (one number per country) is NOT inherently 3-dimensional and is only made to suffer when dressed-up in prism maps and 3D figurines."
Thematic maps in Google Earth: I agree that representing population data on a country scale is not well represented in a virtual globe but I think that other traditional color based thematic maps can be usefully inserted into virtual globes for several reasons:
  • For a small scale thematic map a virtual flight from altitude into the study area conveys information about scale, orientation, location and possibly altitude with the minimum of cognitive load.
  • Draping a thematic map over topography can be a useful visualisation e.g. polygons showing erosion rate draped over a range of mountains, by eye you could then relate erosion to slope.
  • Users can toggle layers on and off to see how geographical elements below relate to a thematic map and fly into areas of interest. E.g. Using a thematic map showing rock temperature at a depth of 10km the user identifies hot areas and then flies in to see how these areas relate to volcanoes in the region.


Frank Taylor said...

I think you're missing some other factors in Google Earth's 3D platform for visualization:

* GE is a 3D visualization platform. You can't animate through a dataset with 2D maps like Google Maps. You talk about thematic maps with 3D symbols being blocked - yet with a Tour you can easily take the user around to different perspectives where the data is all visible.

* The new Tour mode and GE Plugin make it possible to present controlled presentations of the data and add annotations, add narrations, present other data (through overlays and placemark windows), and other multimedia content (videos).

* You can also provide 2D maps (through the placemark windows) along with the 3D views - or side-by-side views with GE and GM.

I believe the GE platform has a lot of untapped resources as a visualization platform, and is now much more versatile for data presentation than it was 3 months ago.

Mark Harrower said...

Hi Rich - I really like your list of 3 additional good uses for virtual globes and all of them strike me as tasks in which the 3rd dimension (and the lay of the land) is an integral part of the map reading experience. I'm not aware of any work to test this, but it would be interesting to know if #2 would be more effect as a 3D GE map or as a 2D map draped over a hillshade terrain map...both would show the relationship between the terrain and the thematic data and I suspect the effectiveness would depend on the map reading tasks (e.g., if they need to estimate slopes, or distance, or...)

Geology applications are where I think virtual earths will really shine (but that's just a hunch) because we've really struggled to show true 3D data (unlike the 2.5D data of the earth's surface, or 2D data of most thematic datasets). Same with the oceans. When the data are rich in the z-dimension, virtual globes make a lot of sense it seems.

p.s. the title of the post was just to get some attention...I'm not normally given to such over-the-top claims :)

Rich Treves said...


You have a point here, it may be that if you present a thematic map in a 3D way and animate with tour/add 2D animations etc users would find it more engaging than a normal colored 2D map. IMHO I think there may be additional problems with this but you have a valid point.

However, what I think Mark and I are both referring to is a easily measurable task e.g.'using this map tell us what the population of the UK is'. In that narrow definition of the usefulness of a thematic map you don't want to introduce extra steps between the user being able to find the country concerned and read off the value. Each of your suggestions adds cognitive load (work) to the user - using the mouse to navigate around other data values, having to scan through a tour or flick eye position between 2 separate maps respectively. Although the work doesn't sound like much its the sort of thing that makes a web page tiring and encourages people to lose interest and, as I'm sure you know from your own web logs, users of the internet lose interest at a phenomenal rate.

To return to an earlier point though, I admit that the narrow task 'read off a value' is not the only reason we are putting data out in virtual globes.

So, as Mark says, I think we need user testing to see what exactly how users react to the new forms of presentation which happens to be exactly what I'm trying to get off the ground at the moment :)

Rich Treves said...

Hi Mark,

I agree that geology presentations are a great application of virtual globes. Interestingly, I have seen some great atmospheric representations of data, I think from NASA which is much the same problem: fence diagrams, models with slices through, that sort of thing. Afraid I can't remember the source for you.

IMHO the ability to fly between scales with the user just immediatly knowing we have switched from continental to m scales is a huge advantage of virtual globes.

In the case of GEarth virtual globes are also a simple layer control system but that isn't a unique characteristic: GMaps allows much the same functionality.

As for attention, no need to clamour for mine :) you'll see from the number of mentions Axis Maps gets on this blog that I rate your work highly