[HOT] Why the HOT obsession with low quality buildings in Africa ?

Ralph Aytoun ralph.aytoun at ntlworld.com
Mon Jul 2 13:46:22 UTC 2018

To help those highly experienced and very accurate OSM mappers understand better what is happening.

I have been a cartographer all my life, but I retired before being retrained and integrated into the world of GIS programmes so I am not as tech savvy as modern day mappers. When I started out mapping with OSM I used Potlach, sitting at home by myself, self teaching as I progressed and, while knowing that the building corners should be squared I did not know that there was a special way of doing this so tried to get as accurate as I could by eye. Until I got a polite message from sev_osm telling me about the squaring facility on Potlach. I was very grateful for that help which made a big difference to my speed and accuracy.

These local people and new mappers that are learning to add detail to OSM do not have the advantage of having a mapping background so have an even steeper learning curve than I did. They are eager, they are keen AND they are willing to learn. So if there are inconsistencies while we are expanding the OSM community into more remote areas then I for one am able to live with that. The fact that the people who are using the data being input (Medicins sans Frontieres, Red Cross, The Clinton Foundation’s Eliminate Malaria Campaign, to name a few) seem to cope with those inconsistencies, makes it reasonable to continue.

Our track record shows that we are gradually increasing the retention rate of new mappers from the original low of 10% and these new mappers are teaching new mappers as well bears good for the growth of the OSM community in those countries.

As has happened in the past and will continue to happen in the future, once those communities, roads and buildings are on the map they DO get added to and improved as local communities grow and take charge of mapping their own countries. If they were not there then there is nothing to improve on or add to, so simply having imperfect mapping is the start to getting accurate maps.

As to using ESRI I am sorry to have to point out that it is not the HOLY GRAIL of mapping and in many parts it is non-existent or low resolution. We do try to map to the latest high resolution mapping available. And switching between imageries is not the best answer because they do not align easily with each other and the rescaling adjustments vary quite a lot so that a building on one set of imagery may be much smaller than that same building on other imagery at the same zoom level. There are also major hiccups where imagery tiles join with offsets of 30+ metres.

So please be patient and allow these communities to grow and adjust to the accuracy of our high tech worlds. Their mud buildings do get pulled down and rebuilt, their unsurfaced roads get rerouted when the rainy season turns the existing road into a quagmire. But inaccurate buildings and roads do help aid agencies get a rough estimate of the population size and how to get there, something they could not do if there was nothing there. These communities are still trying to find out what they have got and where it is.

OpenStreetMap is growing and we have to be patient as other parts of the world try to catch up with us.

Ralph Aytoun
Associate Member of OpenStreetMap Foundation
Voting Member of Humanitarian OpenStreetMap Team
Tutor/Validator Supervisor for Missing Maps London
Member of the HOT Training Working Group
Advisor to West African Motorbike Mappers in Sierra Leone
Validator for Crowd2Map in Tanzania

Date: Mon, 2 Jul 2018 10:24:52 +0200
From: Jean-Marc Liotier <jm at liotier.org>
Subject: [HOT] Why the HOT obsession with low quality buildings in
	Africa ?
Active in Senegal and Mali, I have noticed that changesets tagged with
tasking-manager HOT projects produce very large numbers of buildings.
Those buildings appear to be of very low quality. I wonder: who uses
this data ?

If it is only necessary to assess that people live there, then a
landuse=residential is sufficient

If it is necessary to count the number of dwelling units to infer
population, then a node is sufficient (maybe along with an attribute to
discriminate single or multi-tenancy)

If the geometry is actually necessary, then I wonder if anyone is
satisfied with those semi-random shapes that, with some optimism, may be
identified as being in the vicinity of actual buildings (most of the

Enthusiastic contributors expend an awful lot of effort in flooding the
map with low-quality buildings. I have seen ruins, building parts,
walls, vague shadows on the ground, rubbish heaps, market stalls, cars
and trucks all tagged as buildings - and I'll charitably keep from
commenting on the geometric quality of those that attempt to map actual
buildings (and I'll leave aside the issue of HOT leads requiring the use
of outdated imagery such as Bing instead of ESRI World in Bamako). Is it
the most useful way to channel the energy of inexperienced contributors

I often find myself wishing that HOT leads introduce them to
Openstreetmap through Osmose quality control rather than by churning out
buildings like demented stonemasons trying to reach their weekly quota
of gamified task-managing !

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