Map legends are important in thematic mapping, but KML/Google Earth has no build-in legend support (except the list view of map elements). I think the best workaround is to add a legend using the KML ScreenOverlay element. Unfortunately, this element only supports image overlays and not HTML layers. This makes it harder to create a dynamic legend that changes with your data.
Still, there are options: GD is an open source graphics library for dynamic creation of images. Using this library you can build a legend by adding colour scales and text to an image canvas. GD is written in C with bindings available for various languages.
The legend and map title shown in this screenshot are created using PHP-GD image functions, stored in a KMZ archive as PNG images, and added as screen overlays. You can download the KMZ file here.
Saturday, 31 May 2008
Map legends on-the-fly with GD
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2 comments:
Hi Bjorn,
wanted to email you to discuss your work but couldn't find a link. We've been doing some thematic map development for GE in a humanitarian context but with an emphasis on offline delivery.
http://googleearthdesign.blogspot.com/2008/05/tmapper-thematic-mapping-tool.html
I think your approach is more sophisticated but difficult to deliver offline.
Would be interested to discuss your work with you.
Rich
Hi Rich,
Please contact me on bjorn@thematicmapping.org
It's correct that my approach requires a web server (which could be offline).
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