MasterMaps

Thematic maps are widely used to analyse spatial phenomena in the world. With the rapid development of Internet and GIS technology, people have access to a variety of thematic maps. Nonetheless, these web-based systems often restricts their contents to maps already edited and stored in databases, rather than allowing users to collect data form different sources and create thematic maps meeting their demands. Imagine if a person has a hypothesis about a correlation between number of conflicts and level of poverty in Africa. She wants to see "a map showing the relationship between armed conflicts in Africa and the level of poverty". If she types this into the Google search engine today she might get some useful results, but not the map she is requesting. The search engine is not able to extract the meaning of the query. The results she gets contain all the words she typed in, but the meaning of “relationship” in her request is often about other issues than conflicts and poverty...

Since I'm making my own Thematic Mapping Engine , I need to understand the math behind proportional symbol calculations. Originally, I thought I would need different equations for different geometric shapes, and my book in cartography gave me the same impression. But after reading this article , I realised that life was not that complicated. This tutorial is a summary of a discussion on the CartoTalk forum . I especially want to thank Dominik Mikiewicz (mika) for his valuable comments and figures. The CartoTalk forum is highly recommended! Equations for 1D, 2D and 3D proportional symbols: 1-dimensional symbols (height) This is how the height of bars or prisms is calculated in TME. Equation: symbolSize = (value / maxValue) * maxSize PHP: $symbolSize = ($value / $maxValue) * $maxSize JavaScript: symbolSize = (value / maxValue) * maxSize Bars or prisms show “real” values scaled down to fit on a map, and you can easily see the relations and which is higher than the other. I’m not cons...

3D thematic mapping can be challenging, and I've been considering some of the problematic issues in a series of blog post ( 1 , 2 , 3 , 4 ). There has also been a discussion on the CartoTalk forum , and Rich Treves posted a response on his blog . I released a new version of the Thematic Mapping Engine today as a response to this discussion. The most noticeable new feature is the enhanced colour scale. It's difficult to make a symbol legend in KML, as symbol size varies with scale (zoom). Without a legend, it's very hard to assess the exact values. This is why I duplicate symbology by supporting a colour legend. You can now easily define a colour scale for all thematic mapping techniques. The colour legend informs the user about the range of values (min and max), and where the different symbols are positioned on this range. The colour scale can be unclassed or classed : Equal intervals : Each colour class occupies an equal interval along the value range. Quantiles : The cou...

Ok, this is probably in the " how to sacrifice accuracy for eye candy " category, but it's still fun! Here is Mobile phone subsribers (statistics from UNdata ) visualised using a proportional 3D mobile phone: Mobile phone subscribers in 2003 ( download KMZ ). 3D phone from Mikeyjm/ 3D Warehouse . I'm using volume as the scaled parameter, which I think is more accurate than using area or height. You can even change the colour of the cover... :-o Animated version (1980-2004): Download KMZ (NB! You need a quick computer!) I've added a 3D mobile phone and a 3D person (both from 3D Warehouse ) to the Thematic Mapping Engine , so you can make this visualisation yourself.

The last issue I want to address in my 3D series is the problems of perspective. I find this issue particulary challenging. “Same with estimating sizes of oblique-viewed 3D domes for proportional symbols. The problem is further magnified when the data is re-projected to an Earth globe view making the task of estimating heights/sizes of the polygons even harder (since the user has to mentally compensate for the curvature of the earth). In short their concern is we are sacrificing accuracy for eye candy.” ( Sean Gorman ) Yes, the use of proportional symbols on a 3D globe raises some serious questions. Here are my 3D Collada domes of world population : Download KMZ . At least, the dome shape makes it possible to calculate the volume of each object, as the volume should represent the statistical value. I'm not sure how to scale irregular objects properly, - like a 3D person. The main issue, as stated by Sean above, is how the user are going to estimate the volume of the domes when see...

Since I'm on a 3D choropleth jag , I want to address two common problems with prism maps; blocking and lack of north orientation. “Its possible that a high oil consumption of one country would obscure (or at least complicate the view if the 3D models are translucent) the consumption of a country located behind it, meaning I have to 'fly' around to see the value related to that country.” ( Rich Treves ) I agree with this statement, even though it's possible to guide the user in various ways: In my first and second blog post in this 3D series, I explained why I'm using two visual variables (colour and height) to represent the same statistical indicator. This is another good reason; colour might help the user in identifying hidden prisms. This prism map is created with the Thematic Mapping Engine , and shows life expectancy at birth (both sexes) in 2005. I'm not using a colour scale to represent the statistical value. The prism representing the low life expext...

It’s seems like people have a love/hate relationship with prism maps. Here are some of the arguments in the “don’t like” category together with my counter-arguments: “IMHO creating coropleth maps using prisms is not really *efficient* (but of course it’s spectacular) because it’s really hard (at least for me, maybe I’m too “plain”) to realize slight differences between non-contiguous areas. In fact you are using to techniques to present the same variable, color and prism height. As I see, the classic way to present a quantitative variable using the amount of brightness and just one value (color) is more efficient independently of using a 2D or a 3D environment.” ( XuRxO ) “If I wanted to find out the exact value of oil consumption for a particular country on the thematic map I can easily glance at the colors in the key to pinpoint the value. With consumption converted to height in Google Earth its difficult to read off the actual value.” ( Rich Treves ) “I was talking to some cartogr...