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I've been to a few Missing Maps events now and a lot of the time the task is to trace buildings. I always wonder what is the benefit of mapping the building outline instead of as a single point node? It's a lot faster to map buildings as nodes, and you still get an idea of where dwellings are located. How does the exact size and shape of the building help for humanitarian purposes? |
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Nodes are ok, but you can do a lot more with outlines - one example is we (HOT) got a request for buildings so they could estimate the amount of rubble needing removed. Maybe they could do an estimate with just nodes, but with square footage it's a much more accurate estimation. |
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You can check out the LearnOSM page which provides some more advice and reasoning: https://learnosm.org/en/coordination/remote-tracing/ |
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I would be one that will say to map the whole buildings. And also I just heard why. The reason I am satisfied with is better statistics. It's not just about rubble. You can guess the population based on a building square meters because of a vaccine campaign. Nice story is spraying campaign against mosquitos, and then determining if workers used a predefined amount of spray or they were lazy and work has to be done again. I can imagine some statistics based on buildings shape. Anyway, maps are not just maps, as OpenStreetMap may be used for a wide range of visualization. For some Missing Maps projects I have been told they are indeed estimating population based on size of the building. It can also make it easy to label known buildings, e.g. someone pointing to a large building and saying "that's the school". Another project was using pre-disaster imagery to map building outlines, followed by a project using post-disaster imagery to tag the buildings(ways) as okay/damaged/flattened. For the latter project, you'd want to know the outline of the building. I had not heard about estimating the rubble needing to be removed that @russdeffner mentions.
(14 Dec '18, 19:21)
LivingWithDr...
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This is speculation, but you could assume that a bigger building is probably stronger, and that its inhabitants are probably richer. Also, you might be able to assume the function of a building from it's shape, in the way that Medieval European churches commonly were cross-shaped. Long, rectangular buildings close to an open area are often schools. |
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Another speculation: Even if there currently are no aid organisations that are using the building shape and size, it is not unimaginable that they would want to do that in the future. And while enhancements to OpenStreetMap normally are progressive, meaning you add information (building height, function, material) to existing objects, going from nodes to outlines requires re-drawing every building. So if we would be quick now by drawing buildings just as nodes, then in a possible situation where there is demand for building outlines, we would have to start all over again. |
That's a good question - but I'd suggest that the place to start is the person saying that to you at the next missing maps event. Presumably the person advising people how to map got that advice from someone else (and they got it from someone else, etc.), but eventually there'll be a reason why they are suggesting to do it that way.
I could guess a few possible reasons, some very valid and some less so, but speculation wouldn't really help I don't think.
Also mapping buildings as nodes would reduce topology errors very often encountered in humanitarian mapping projects: very poor building shapes, overlaps, offset... This would be easier for beginners mapping on tasking manager projects. More experienced mappers may come later and add the outline correctly.