[HOT] Validation queries

Theodin theodin at posteo.de
Wed Jan 15 10:21:00 UTC 2014

Hi Severin and all others,

Although I practically stopped working on OSM in CAR, I am still following the list and read your
Wiki-page-style how-to with interest (reading it I realised I didnt make any of the errors you
mentioned which is nice :) ). I hope to be able to contribute more in the coming months. Its nice to
see so many people emergency-map for OSM (Yolanda etc), and I hope some will start to work on other
areas as well which are hit badly by crises of a not-so-obvious nature.


Am 14.01.2014 19:24, schrieb Severin MENARD:
> 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 <mailto:nick.allen.54 at gmail.com>>
>     To: HOT at openstreetmap.org <mailto:HOT at openstreetmap.org>
>     Subject: [HOT] Validation queries
>     Message-ID: <52D29D10.6010009 at gmail.com <mailto: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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> HOT at openstreetmap.org
> https://lists.openstreetmap.org/listinfo/hot

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