[HOT] Blog post on the mapping to support Support the Disaster Response in Malawi Flooding (Severin Menard)

Severin Menard severin.menard at gmail.com
Fri Feb 27 17:21:22 UTC 2015

On Fri, Feb 27, 2015 at 2:07 PM, Kretzer <kretzer at gmx.net> wrote:

> Thanks, interesting post!

> Will the mapping be evaluated by the local volunteers? I guess there is
> some cleaning needed, and a lot of decisions can't really be made from the
> aerial imagery. Like the classification of the roads,

I would say it is easier to classify the roads from the imagery because you
can figure out more easily the respective hierarchy between them. Eg it
seems there are more unclassified and tertiary roads than eg in CAR where
you have the main roads and mostly just tracks

> for example, or often you can't tell if something is really a building, or
> if its used for living (more so, where the imagery is not so clear).
I also need to make a pic album for everyone to understand better what is
what (starting now), but mapping all the buildings, even the smaller ones,
make sense. Basically the households have generally two houses : the main
one (that can have a metallic roof or not and can be rectangular or
squared) is the residential one; the smaller one close to it is the most
often the kitchen or can be a shelter for pigs or other small animals. Dark
brown are corals for cattle, closed by a fence. Toilets are a small
building too, generally a bit distant from the house. the Shower has not
roof, it is a kind of snail shape (no door but you can - obviously cannot
see the inner from outside) in light material, but you cannot see it on the
imagery unless there are shades

> I quite unsure how to handle the buildings that were tagged as nodes.
> Sometimes I could see to which buildings they belonged I included the node
> in the building outline, so that the tag information wasn't lost (I hope
> this the correct way of doing this ...). Often this is impossible, though,
> as there are lots of small buildings, often blurred, and lots of nodes. But
> if the outlines are added, many buildings would be counted twice. So is it
> best to do nothing where the survey was done on the ground and only ad
> buildings outside the tagged areas?
> This is the first time I have done this, so maybe I'm overly confused ...
No it is confusing, because we had no imagery in some areas when we started
so we mapped buildings as nodes. If you can replace the geometry node ->
polygon with iD (it is unfortunately not possible with the JOSM
utilsplugin2), go for it when it is obvious. Buildings remained nodes even
with the imagery for the smallest buildings (and buildings can be small in

> Also it would be very useful to see the date when the images were taken,
> so we could tell e.g. which is the newer iamge, where more than one is
> available. Is that technically possible? (the BING images say (C)2015, but
> I'm not sure that means the photos were actually taken in in 2015).
in JOSM, you can right click and click on Show tile info. In Lower Shire
Bing imagery is generally from August 2011. Where are you mapping? Close to
the lake or there?

> ------------------------
> Hi,
> With the Help of Charlotte, Cristiano and Blake, I published on the HOT
> website this blog post presenting an overview of both the disaster and the
> OSM mapping to support the response with pictures provided by the HOT
> interns in Malawi There are two ongoing Tasking Manager jobs, one almost
> done and the other one just starting. Please read, join and contribute!
> http://hot.openstreetmap.org/updates/2015-02-27_hot_called_upon_to_support_disaster_response_in_malawi_flooding
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