Skip to main content

Making proportional symbols in KML

I would argue that KML and Google Earth supports reference maps (geographic features) much better than thematic maps (spatial patterns of a theme). Still, there are some workarounds, and this week I want to show three different ways of making proportional symbols in KML: icons, regular polygons and collada models.

In this post, I want to focus on how to make proportional circles using the KML Icon element. This is the easiest and most efficient way to make proportional symbols.

This map shows the population in each country of the world in 2005 (source: UNdata). See this blog post for information about symbol placement and how they are mathematically scaled.

A KML icon has to be an image. I hope vector support will be added in the next major KML version. A circle can be drawn using one line of SVG, and I think KML should support such basic shapes. Still, KML has powerful ways of styling icon images, and I've used these elements to create proportional symbols.

I've made one icon for the proportional symbols map. The icon is a white circle on a transparent background saved as a PNG file (200 x 200 px). The icon size has to be bigger than "normal" icons since it will be scaled proportional to an attribute value. The icons are colourised and scaled using IconStyle elements. Only one image is thereby needed to make circle symbols in different colours and sizes. The KMZ file containing KML and the image is only 19 kB.

The drawback is that the map is only viewable in Google Earth (so far). This is how it looks in Google Maps and Microsoft Live Maps (Virtual Earth). The icons are not colourised or scaled.
Labels:

Comments

Anonymous said…
Hi Bjoern,

could you please explain where you got the landscapes overlay for GE shown in the first picture?
28 April 2008 at 09:33
Anonymous said…
Sorry,
now I see: It's Natural Earth II. OK, but you have a broken link or missing PNG over Western Europe.
Thanks, Lars
28 April 2008 at 09:43
Bjørn Sandvik said…
Hi Lars,
Yes, it's Natural Earth II from this blog post. I'm working on my own basemap for thematic maps, as I find the Google Earth satellite imagery too "cluttered". All tiles seems to load here, please send me a screenshot: bjorn@thematicmapping.org
28 April 2008 at 10:28
Anonymous said…
Hi Bjørn,

The concept should work in Google maps if you include the styling "inline" with the placemarks, instead of as a reference to an included global or external style file. Of course your KML will get bigger as a result, but at least the styling should work.

Google Maps needs to have the style specified in each placemark definition, while Google Earth can do either in0line or global styles.
24 November 2010 at 21:39
Post a Comment

Popular posts from this blog

Creating a WebGL Earth with three.js

This blog post will show you how to create a WebGL Earth with three.js , a great JavaScript library which helps you to go 3D in the browser. I was surprised how easy it seemed when reading a blog post  by Jerome Etienne . So I decided to give it a try using earth textures  from one of my favourite cartographers, Tom Patterson . WebGL is a JavaScript API for rendering interactive 3D graphics in modern web browsers without the use of plug-ins. Three.js is built on top of WebGL, and allows you to create complex 3D scenes with a few lines of JavaScript. If your browser supports WebGL you should see a rotating Earth below: [ Fullscreen ] To be able to display something with three.js, you need three things: a scene, a camera and a renderer. var width  = window.innerWidth,     height = window.innerHeight; var scene = new THREE.Scene(); var camera = new THREE.PerspectiveCamera(45, width / height, 0.01, 1000); camera.position.z = 1.5; var rende...
11 comments
Read more

Thematic Mapping Engine

It's time to introduce the Thematic Mapping Engine (TME). In my previous blog posts, I've shown various techniques of how geobrowsers can be used for thematic mapping. The goal has been to explore the possibilites and to make these techniques available to a wider audience. The Tematic Mapping Engine provides an easy-to-use web interface where you can create visually appealing maps on-the-fly. So far only prism maps are supported, but other thematic mapping techniques will be added in the upcoming weeks. The engine returns a KMZ file that you can open in Google Earth or download to your computer. My primary data source is UNdata . The above visualisation is generated by TME ( download KMZ ) and shows child mortaility in the world ( UNdata ). The Thematic Mapping Engine is also an example of what you can achieve with open source tools and datasets in the public domain: A world border dataset is loaded into a MySQL database . The same database contains tables with statistics ...
45 comments
Read more

Creating 3D terrains with Cesium

Previously, I’ve used three.js to create 3D terrain maps in the browser ( 1 , 2 , 3 , 4 , 5 , 6 ). It worked great for smaller areas, but three.js doesn’t have built-in support for tiling and advanced LOD algorithms needed to render large terrains. So I decided to take Cesium for a spin. Cesium is a JavaScript library for creating 3D globes and 2D maps in the browser without a plugin. Like three.js, it uses WebGL for hardware-accelerated graphics. Cesium allows you to add your own terrain data, and this blog post will show you how. Impressed by the terrain rendering in @CesiumJS - with a 10m elevation model for Norway! Farewell Google Earth. pic.twitter.com/RQKvfu2hBb — Bjørn Sandvik (@thematicmapping) October 4, 2014 Compared to  the dying Google Earth plugin , it's quite complicated to get started with Cesium. The source code is well documented and the live coding Sandcastle is great, but there is a lack of tutorials  and my development slows down when ...
12 comments
Read more