Thanks for the additional info, that makes things a bit clearer. Based on this it seems your suggested tagging is not right. You base the classification into waterway types on the HYP attribute - which is not what this indicates apparently.
More generally speaking i have doubts about the wisdom in importing large parts of the data. Looking over it a large fraction of the waterways in the data set are not correct. This is already hinted in the information you provided. Most of the waterways (more than 40k, i.e. more than 90 percent) are indicated to be dry, that is without any evidence of present day water flow. Looking over the data i could find a lot of cases where a drainage shaped landform was interpreted to be a stream and that stream was then continued downhill without any physical indication of even historic water flow - sometimes along tracks misread to be streambeds, sometimes also right across villages and other human built structures. In subtropical Africa it is very common that due to climate change (both recent human made and natural changes over the last few thousand years) as well as immensely intensified groundwater use valleys created by water flow - with often indications of that visible in imagery - do not carry even sporadic water flow any more at present time. This is called a fossile waterway. According to OSMs verifiability principle mapping such structures as waterway however is clearly wrong. The problem i see is that importing such data where a large portion of the features are factually incorrect will either result in * a lot of incorrect data in serious need of cleanup imposing a serious debt on the local community. * a lot of work to evaluate every single one of the >40k features to assess if it really represents a verifiable waterway. My estimate would be that this work might be more efficiently invested in mapping those from scratch. Now this of course varies a bit across the coverage area - in the western part a significant fraction of the HYP=4 waterways show indications they could be legitimate intermittent streams based on available images (though you often have to spend a lot of time looking for hints for that). In the east this is much less so and i would probably consider the majority of features bogus. At the same time the positional accuracy of many of the features is poor with positional errors in the order of often 50-100m. This is another indication that importing this could be quite wasteful in terms of time spent. Overall i would probably say that for mappers invested in improving the area this data could be useful to help identify where there are possibly waterways to map. But as an actual import where the mapper just does a quick verification and tag adjustment before adding the feature more or less as is it seems less suitable. And actual import would bear a high risk of well meaning mappers adding a lot of incorrect data because of the principal difficulty of proving a negative (it is hard to reliably prove a waterway from the data does not exist in reality and many likely will be inclined to trust the data being correct in such cases). Existing waterway data in the area is - while being incomplete - fairly decent quality it seems and it would be unfortunate if that was diluted by low reliability data. -- Christoph Hormann http://www.imagico.de/ _______________________________________________ Imports mailing list [email protected] https://lists.openstreetmap.org/listinfo/imports
