MasterMaps

The work is done! Today I could finally hand in my MSc GIS thesis: "Using KML for Thematic Mapping". From the abstract: The use of geobrowsers has increased considerably over the last few years. Thematic mapping has a long history in cartography, but the new geobrowsers (like Google Maps and Earth) tend not to focus on this aspect of geographical information representation. This paper examines how Keyhole Markup Language (KML) can be used for thematic mapping. KML is not targeted towards thematic mapping, but it is possible to use KML elements in ways that were probably not intended. Current possibilities for making proportional symbol maps, chart maps, choropleth maps and animated maps with KML will be presented. These experiments show that KML and geobrowsers offer great potential for thematic mapping, but that there are significant issues that need to be resolved. Thanks to everyone who has given me valuable feedback and advice during these months! Stay tuned!

If you use the World borders shapefile provided on the site to create a KML prism maps , you will experience a problem. The same problem is likely to occur if you extract polygon features from other shapefiles. The prism map will look like this in Google Earth: The prisms are not colourised properly. The reason turned out to be the clockwise orientation of the polygon vertices (winding order). 3-D implementations of KML use the vertex winding order for determining the direction in which it faces. This is necessary to display the correct lighting on curved surfaces. For the prisms to be displayed properly the vertex order has to be anti-clockwise. The prisms will be colourised properly by simply changing the direction of the coordinates. The light has been switched back on. The vertex order was changed by this PHP function: function kmlReverseCoordinates($coordinates) {   $coordinates = explode(" ", $coordinates);   $coordinates = array_reverse($coordinates); ...

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...