[HOT] Validation queries

Tue Jan 14 18:24:18 UTC 2014

Hi Nick,

Thank you for your email. My answers inline.

> Date: Sun, 12 Jan 2014 13:48:00 +0000
> From: Nick Allen <nick.allen.54 at gmail.com>
> To: HOT at openstreetmap.org
> Subject: [HOT] Validation queries
> Message-ID: <52D29D10.6010009 at gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"; Format="flowed"
>
> Hi,
>
> Would you like me to join in with the validation process? I am
> experienced in mapping OSM, but am fairly new to regularly mapping HOT
> projects.
>
Would be great! Thanks for the proposition! Indeed you have contributed a
lot in OSM. Mapping HOT projects is not very complicated, as you saw with
the Highway_Tag_Africa<https://wiki.openstreetmap.org/wiki/Highway_Tag_Africa>,
it is less detailed then in developed countries, at least regarding remote
mapping. Maybe the difficulty is when you do not know how those contexts
look like. A goo way to compensate this is to look for videos posted on
Youtube (examples
here<http://www.youtube.com/results?search_query=bangui&sm=3>),
especially the ones taken along road or streets. This is how you figure out
if properties enclosures are walls, fences or hedges, what is often a
cultural feature. Ah, just saw you mapped some wall enclosures (eg
here<http://www.openstreetmap.org/node/27564988#map=19/4.41952/18.51870>).
They actually are buildings (houses) under construction. It is frequent in
developing countries that such works last a long time or even be abandoned.

>
> I'm responsible for some of the mapping in
> http://tasks.hotosm.org/job/72, as well as trying to change some of the
> more obvious 'highway=track to highway=residential or unclassified etc..
> or it may be easier to check what I've done using my OSM profile
>
> http://www.openstreetmap.org/user/Tallguy/history#map=13/4.4168/18.4936&layers=N
>
> How much validation is actually needed / done? Is it a proportion of the
> whole task, or just until you are confident that, all things considered,
> the task is fulfilled? You're never going to get 100% as some things
> boil down to opinion about what the images actually are of, but the vast
> proportion is pretty obvious.
>
This is something that still needs to be settled and documented. I would
say a validation is about both identifying mistakes/mapping lacks and
standarzation/consolidation and has 2 or three steps, related to scale:
1. At neighborhood scale, check notably if:

   - buildings are missing. Sometimes it happens and if actually it
   represents a consequent number of building over a TM task, it can be
   invalidated
   - buildings are correctly traced. Hopefully it is not frequent, but
   sometimes mappers made really coarse outlines that do not respect either
   the buildings proportions or angle. More frequent are mappers that do not
   know how to square the buildings. In this case, after having checked what
   is their preferred editor, I generally send a message to their OSM message
   box to give them the tip to do it
   - highway tags are correct. This is what you described. Some mappers put
   tracks wherever it is not a main road considering it is not paved, but this
   is not a meaningful criteria in these developing countries considering 99%
   of roads are unpaved.
   - road geometry. Some mappers do not put enough details and other too
   much (eg a node every 10 or 20 m even if the road is straight). First case
   is quickly corrected with the (magical) Improve Way Accuracy mode in JOSM;
   second case requires deleting extra nodes when they actually make weave a
   straight road.
   - start/end of roads. Some mappers are experts of giant snake roads or
   loop roads, Requires to pass the mouse over the streets to see their extent
   and cut them where it makes sense. On the contrary, some streets or roads
   are sawed without any reason (same tags for all the sections)
   - general issues of connections between objects. Some that should be
   connected and those that should not. Requires both Validator and also eye
   control

 2. at the town or city scale, it is quite related to the road network and
its main highways. Having a larger view  to identify the highways that are
not simple residential roads. They are often larger and frame a larger area
or can be a parallel way to main roads. It is also important to check where
they start and when they stop, what is often not possible to do when you
map with the Tasking Manager. This is what I tried to do with
Bouar<http://www.openstreetmap.org/#map=14/5.9374/15.5879>;
here are some examples of issues for Bangui:

   - missing parts of
highway<http://www.openstreetmap.org/node/27564988#map=17/4.38964/18.54186>.
   Looks weird on Mapnik and the check of the imagery confirms the two sides
   of the road separated by a drain are not finished
   - road continuity<http://www.openstreetmap.org/node/27564988#map=17/4.38686/18.50796>.
   The situation here seems weird as well as we expect the 2 unclassified
   roads to be connected and not joined by a simple path. The imagery confirms
   that the southern highway looks the same, and should be tagged the same,
   whatever the tag. The example is actually good as farther
south<http://www.openstreetmap.org/node/27564988#map=17/4.37643/18.50931>,
   it changes for tertiary. No reason for this, says the imagery. It should be
   cut when it becomes a straight road, though
   - isolated upper-level road
sections<http://www.openstreetmap.org/node/27564988#map=15/4.4070/18.5068>.
   Drivable highways cannot be isolated and connected to the drivable road
   network by paths, they must be connected to it
   - tagging coherence <http://www.openstreetmap.org/#map=15/4.4333/18.5314>.
   in this example, the primary and tertiary road are connected by a
   unclassified road. Same thing between the two tertiary roads. After having
   checked the imagery this road would deserve to be tagged as tertiary. This
   obvious example apart, this requires to check the streets width to identify
   the main ones that needs not to be tagged as residential but unclassified
   or even tertiary.

Hope this can help! I had in mind to give some tips and it became a start
for a future wikipage :) Hope other people will read/discuss/complete this.

Sincerely,

Severin

Any constructive feedback from experienced HOT mappers is welcomed.
>
>
> Regards
>
> Nick
>
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