[HOT] Fwd: mapping standards

john whelan jwhelan0112 at gmail.com
Sun Nov 9 18:49:01 UTC 2014

I'm currently mapping #684 - Polio outbreak and Ebola preparedness,
Meiganga, Cameroon and I must confess I have questions about the project.

I can understand French especially a European or African accent so the
video was useful to some extent.

To me HOT is different to normal OSM.  In normal OSM people basically do
their own thing.  Sometimes they use "standard" tags but there is a wide
range and style of tagging.

HOT prepares maps for a particular target audience so to my mind takes a
more standarised approach.

What I haven't seen is a list of requirements.

There is a list of tasks but that isn't the same as a list of requirements.

For Meiganga there are thousands of buildings to be mapped.  I understand
the idea that ideally each building outline shape should be carefully
mapped but realistically with the JOSM building tool I can approximate the
building size in two or three seconds.  To carefully trace the outline
takes me twenty seconds or so.  If I look at some tasks I see someone has
mapped three buildings then given up.  They are beautifully mapped but when
there are another 98+ buildings to map in the task and another 180 odd
tasks to do?  Yes we are using volunteers so their time doesn't cost us
anything but mapping buildings is tedious and how fast do we want the
information to be made available and how accurate do we need it?  What
exactly is the requirement?

I think for this you need to go back to the AID agencies and the Cameroon
government cartographers and get them to make a list and set priorities.

Can we tackle the tasks differently?  The road network and water really
need to be done first.  It's better to have as few a number of segments in
a read as possible.  That way when you tag the name you only need do it
once.  Water, in a task its difficult to see if its a river, ditch or a
clump of trees sometimes.  From further out you stand a better chance.

Also if we break the tasks down then the grunts, sorry less skilled
volunteers, can tick off the task as done when they've mapped all the
houses and paths.  If they are daunted by the idea that they have to map
all the "residential and non-residential" buildings and forests before
marking the task done they maybe reluctant to tick the box and we end up
with lots of tasks mapped but not ticked as done.

Then we get to the quality of the map.  It sounds dumb but different
satellites have different accuracy.  DigitalGlobe’s WorldView-2 is one of
the better ones.  There was presentation by *Kevin* Bullock on the subject
at a SOTM US recently but the video seems to have disappeared.  If you can
find it the relevant bit is 15 mins in for 90 seconds.  If you look at in
task 684 you'll notice that the Bing imagery and the Mapbox imagery don't
quite line up.  Some mapping has been carefully done from Bing and some
from the DigitalGlobe imagery.

Can we clean the data up?  Interesting question, from a satellite imagery
I'm unable to tell if a building is residential or not, however many
buildings mapped from satellite imagery are tagged building=house rather
than building=yes.  I would suggest that if building=house is tagged from
satellite imagery this be changed to building=yes by bot but only if its
the initial tag on the building.

Some small blobs might be a car or an outhouse.  Perhaps it might be
worthwhile to scan for a minimum size building?

If we go back to the idea of requirements again it seems likely that to get
a better map we need someone on the ground.  worldbicyclerelief.org do
reasonable bikes for Africa, I'm from a technical background so I like the
idea of some sort of computing device to enter data on. Smart phone perhaps
or can we work with one of the local schools?  I assume that Internet
access is not ideal but text messaging might work.  I'd envisage
compressing / encoding the information so it fitted into the constraints of
text messaging to get the updates back.  It would need some programming
effort on the device and at the other end but there are a large number of
programmers around OSM.  This may well be already sorted out but as a
mapper I'd like to think that my efforts were used rather than left waiting
for someone on the ground to do their bit.  I might even dump some cash
into a charity that could sort this sort of stuff out and yes I know its
not as instant as a bag of flour but it is important to have the
infrastructure in place.

Cheerio John

On 9 November 2014 10:53, Pierre Béland <pierzenh at yahoo.fr> wrote:

> About the video of the Eurosha volunteers, I forgot to add the link.
> This is https://www.youtube.com/watch?v=saFsT558Xbo
> Pierre
> _______________________________________________
> HOT mailing list
> HOT at openstreetmap.org
> https://lists.openstreetmap.org/listinfo/hot
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