OpenStreetMap

Quality of river mapping

Posted by Gerhardus Geldenhuis on 30 January 2013 in English (English)

I just realized that the Vaal river in South Africa, which has been mapped by different people has been mapped using Bing and CD:NGI imagery. This is not necessarily a problem in itself apart from the fact that in places the Bing imagery were taken during flooding and does not represent the normal flow of the river. There is thus some work required to differentiate this. In a previous diary entry people have suggested using a flood plain tag. It might be appropriate but only if it is a regular occurrence which I am not convinced it is. I will need to spend some time comparing exceptional flood event dates with the imagery dates and then make a decision on the frequency of occurrence to guide the choice in tag being used. Since I mapped a large part of the Vaal river, or at least it's river banks, this diary entry is more of a note to self, to do the work at some stage.

The most used tag seems to be: flood_prone

Location: Tokologo Ward 4, Tokologo Local Municipality, Lejweleputswa District Municipality, Free State, RSA

Comment from HeBri on 31 January 2013 at 11:36

Hi Gerhardus, just to let you know: In the German weekly notice it says that http://aerial.openstreetmap.org.za/ now provides areal images of South Africa with 50cm resolution. I haven't had a look myself so I don't know in what flooding state these were taken. But may be these are useful for you? Just to make sure you get this information. Kind regards from Germany Heinz

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Comment from Gerhardus Geldenhuis on 31 January 2013 at 19:18

Thanks HeBri, the imagery you mention is the CD:NGI imagery I referred to.

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