Just to clear up a bit of a misunderstanding about the helipads too. There is a tag aeroway=helipad for ‘proper’ helipads which we do use when appropriate. The leisure=common thing is being done because many small villages have a common area near them and this are can so happen to make a good place to land a helicopter, just like a soccer pitch or other large grassy area. So we are not tagging them incorrectly, rather we are tagging them correctly just the reason we are placing focus on them is their potential use for helicopters.

Regarding the size of the common areas, just map them as they actually are, and it will be up to anyone using them to assess their suitability for what they may want to land there. Also, another fringe benefit of having them mapped is even if they aren’t used as landing sites, they make great places to park a truck to distribute food/medical supplies, or hold a community education meeting, etc. So it is their ancillary uses that makes them initeresting to us at this particular time.

Hope this clears up the confusion. I know there was a lot of confusion about this tag.

-AndrewBuck

Yeah, I plan to try to make the channel width and profile variable so that the original dem cut very roughly with the streams to force the dem to drain properly in the areas where we know how it should drain. Then run the drainage calculation and use the results to determine the signifigance of each stream. Finally, knowing this go back to the original dem and re-carve it, now using variable stream widths.

-AndrewBuck

@JohnDoe23 Yes I am aware of the aretfacts, I think forests is a big part of why there are a lot along rivers because that is where the trees grow best due to the water. I do plan to take many things from OSM into account, not just landuse, but more sophisticated things as well, for example railroad tracks act much like a contour line since they cannot run at a steep grade, so you can gather elevation info from them just like you can with streams, etc.

@imagico Those are very interesting posts and I want to read through them all again in more detail. It would be very interesting to talk to you about this, can you connect to mumble (talk.hotosm.org) sometime or contact me on skype (my username there is the same as my name on this site except with a ‘40’ at the end of the name)?

-AndrewBuck

@Hedaja @mcld Yes, in theory you can get elevation from GPS traces but there are a lot of problems. What I am trying to do is to take a different approach. Rather than trying to determine the absolute elevation of each pixel accurately, I am more interested in using the “hints” that the OSM data gives us about the relative elevation of a pixel to other nearby pixels. The ASTER and SRTM data are already pretty good once you get up to more broad scale elevation (beyond about 100 meteres or so), this is just to fill in the details and make them more suitable for really small scale mapping applications like high zoom level contour lines or for things like flood simulation, or terrain models for games, etc.

Regarding this “relative” elevation hints, this work grew out of an idea I have been working on for a long time. I started trying to document some of it a while back at the following wiki page. Feel free to add any other tags that might be relevant. Don’t worry about filling in the other columns if you don’t understand them, but anything that might tell you about the elevation of the ground either below or nearby the mapped object.

osm.wiki/OpenTerrainModel

@Nick I added the elevation difference from the carving, that was a great idea, it will really help me understand where my algorithm works and doesn’t work going forward.

-AndrewBuck

Yes it would be possible. It is important if you do this though to make sure all the landuse=residential areas are drawn around the villages in a consistent manner. Have a look at how Pierre and I do the borders around the villages in the southwest region there and that should give you a good idea how to do the borders to keep it consistent. Since the bulk of our analysis is based on the area of the village, making that polygon fit nicely is very important.

For the test villages I don’t tag the number on the area I just map the actual buildings and huts in OSM and then use QGIS to count how many buildings are in each residential area. I can help you get started with building tools if you are interested in mapping the test villages to seed the density calculations.

-AndrewBuck

Also known as “null island”. A lot of stuff ends up there. Not just GPS traces but nodes, etc. You also see a lot on the equator that obiously don’t belong there where just one coord got 0.0 and I assume the same happens along the meridian. I have also heard the poles collect nodes too but haven’t seen it myself.

-AndrewBuck

Having a bot remove single nodes is not a good idea. The redaction bot left those nodes behind on purpose, to help future mappers re-create the missing data. There were pros and cons but the debate was had and ultimately decided to do it this way. It is good that you are interested in seeing them cleaned up, but unfortunately a careful manual approach is needed, not just a quick bot run.

Regarding the node in a building thing, I agree and I think that is the general consensus as well. If you try out josm, you should check out the ‘replace geometry’ function in utilsplugin2 is very good for “upgrading” nodes into areas.

-AndrewBuck