Here's my problem (and I was inspired to ask this from this question)...

I create a KML file recording where upcoming training courses will be for the next year. The cities might be Atlanta, Calgary, Toronto, Dallas, etc

So I can automate the process, I read the list from a file, use a geocoding service to get the coordinates of "Atlanta" and insert a placemark at that point. Now a user can open the KML and see there is training in Atlanta.

However, what if that user zooms right into Google Earth, uses the placemark to identify a particular building, and assumes the training will take place there!

I can't give the exact building location, because it won't be booked till closer the date. But how do I tell my user that the placemark is only meant to signify position to the city-level, and not right down to a particular building?

Should I fiddle about with zoom level displays, use a polygon instead of a point, or is there a good KML method to solve the issue?

  • Would a description balloon stating the above details not suffice? – Andy W Feb 8 '11 at 3:07
  • geocode to 6 decimal places in decimal degrees will be accuarate enough. – Mapperz Feb 8 '11 at 15:11

IMHO best to approach this from a cartographic viewpoint before thinking about the tech implementation.

Cartography: You are quite correct that a polygon makes more sense than a point as you are actually marking an area. However, a polygon isn't visible from a great altitude, pins (or the point icon you choose) in KML remain constant in size over a certain range in altitude and that is probably helpful to you. The best combination IMHO would therefore be a point that fades out as the user drops in altitude whilst fadeing in a low opacity polygon with no hard border (gives the user a sense of 'rough region'). I would suggest the polygon to choose is a blue circle as this is what the iPhone uses to show when it is not sure of your location - perfectly sound way to do it and what a number of your users will have seen. E.g. http://www.reseo.com/blog/iphone-maps-gps-local-search-results-and-mobile-advertising

Tech: The way to do this in KML is regions: http://code.google.com/apis/kml/documentation/kmlreference.html#region

Create a placemark/polygon pair for each location and program them using regions with an appropriate fade in/out behaviour.


Could you use a polygon to identify the area (with a very low opacity level) so that it suggests an area, rather than a specific location?

As an aside, CityGML deals with this issue by formalizing Levels of Detail (LODs) for 3D buildings. It's not quite relevant for marking city boundaries (I think) as it focuses more on the building / neighborhood level.

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