Andrew Wilkinson

Random Ramblings on Programming

Crowd Sourcing Mapping

with one comment

GPS Status app - HTC Desire by avlxyzRecently Google announced that they were making their crowd sourcing mapping tools available to users in the United States. This tool lets uses edit Google Maps, adding businesses and even roads, railways and rivers. This raises interesting questions about whether wisdom of the crowd can be applied to data that requires a high degree of accuracy.

Open Street Map has been doing this since 2004, and has put together an amazing resource of free map data, but only recently has Google begun to allow people to edit its maps for large parts of the world.

Accurate mapping data is terribly important. While the majority of Google Maps queries are likely to be “how do I get from my house to my aunt’s?” some are much more important. A war was almost caused when the border between Nicaraguan and Costa Rica was incorrectly placed. While a war is a little far-fetched, it’s not hard to imagine how a mistake on map could cost someone’s life in a medical emergency.

Originally Open Street Map required budding cartographers to get out with their GPS devices and manually record their position. With the explosion of satellite* mapping information creating maps just involves sitting at your webbrowser and clicking. But how accurate are the satellite images? It’s easy to find a road on Google Maps that disagrees with the imagines underneath it. It’s not so easy to work out which one is correct. The height and angle of the terrain, the location of the plane and other processing errors may make the satellite imagery not line up with GPS data.

Like most crowd sourced data sources Google’s Map Maker and Open Streetmap have a voting process so vandalism will be weeded out, but for people sitting at their computers looking at the same, possibly misleading photos, it won’t improve the accuracy of the changes.

Without knowing more about the collection process for the satellite imagery it’s hard to know what level of accuracy they have. Presumably it’s pretty good, but we need to decide how accurate maps need to be. When you’re looking a country level map even a kilometer here or there doesn’t matter too much, but get down to the level of a walker and suddenly centimeters become important.

What’s more important, masses of mapping information or accurate maps? I’m not sure, but I think it’s probably the latter.

If you want to see the mass of data that is being created by the crowd, Map Maker Pulse is a fascinating and hypnotic site to visit.

The final issue is that of licensing. Open Street Map is very clear that any time you spend improving their maps is rewarded by your work being released under an open source license. Google’s terms of service require you to given them a license to do whatever they like to your work. They do not need to make your changes available for others to use. Google is asking you to do high precision work for free and then taking that work and locking it inside in Google Maps, and that doesn’t seem like a fair trade to me.

* Hopefully no one is actually using imagery from a satellite for mapping, but rather photographs taken from a plane.


Photo of GPS Status app – HTC Desire by avlxyz.

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Written by Andrew Wilkinson

May 20, 2011 at 1:59 pm

One Response

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  1. Totally agree-and the Google maps data is so poor in many places compared to OSM. So the only Android OSM Google maps replacement that I found that works at all is MapQuest. Any better suggestions?

    George

    September 23, 2011 at 8:44 pm


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