[HOT] So you’ve thought about becoming a validator.

john whelan jwhelan0112 at gmail.com
Mon May 23 01:46:51 UTC 2016

HOT has a two stage process unlike OSM where you simply map.  The idea
behind the two stages is to improve data quality.  So how good a mapper do
you need to be to become a validator?  A total expert in all things, or
something less?

In HOT we are normally interested in where do people live and how do we get
there.  So settlements, sometimes buildings and highways. How rough are HOT
mappers without validation?  Some aren’t too bad, some omit buildings on a
buildings and highways project, some omit highways but put the buildings
in.  The tags can be all over the place, sometimes correct sometimes not
correct.  I’ve seen a new mapper mark half a dozen tiles mapped with
nothing on any of them tagged with their name.  So even rudimentary
validation is extremely valuable but recognize you get no recognition for
it.  No record of the number of tiles validated is kept.

If we catch a mapper early in their mapping career with a bit of feedback
then they tend to correct themselves and map according to the way we’d
like.  Invalidate them and the negative vibes can turn them off mapping.

How much experience do you need?  I’ve seen someone with three months
experience do a very reasonable job on simple projects.  It helps if you
have another validator you can check back with.  You need an eye for
detail, and you need to be able to accept that somethings were mapped
before HOT tiled the area so you have to follow the OSM rule which is more
or less unless you’re on the ground you do not delete or modify in a major
way. <crtl>i will give you the date mapped and the mapper’s OSM name by the
way so if it’s a year old leave it alone, if its mapped in the last two
weeks its fair game.

The tools, you need JOSM, nothing else has its capabilities for validation.

Read the project instructions very carefully, if they want you to map
everything in sight go and look at another project.

The aim is to catch the major mistakes, the untagged ways, the buildings
tagged area=yes, the crossing ways, the highways that almost meet, in
Africa the highways between settlements that are tagged as tracks.  You’re
looking for the tiles that have less than 50% of the mapping done.  You
don’t need a PhD in validation to do these.  Squared buildings I feel is a
religious question.  If its roughly in the right place should you square or
not.  If you feel you should then in JOSM if you see a bad one you can
search for buildings with less than 7 nodes, sub-select the mapper and hit
q to square all of them at once.

You are only validating against the project instructions so if it asks for
buildings and highways and someone has mapped a couple of dozen buildings
don’t invalidate it because some buildings are missed.

I scan at a lower resolution than I would use to map, I’m thinking more
about putting things right than catching every tiny mistake.  JOSM allows
you to move up and down the tile vertically with <crtl><down> etc.
Buildings invariably have paths or highways leading to them so that gives
you a clue where to look.  Zoom in at likely spots to check for details.

Highways are a bit subjective, is it a path or unclassified? well I expect
the locals to refine the map so as long as something is there its probably
OK.  Note that in Africa highway=footway is not used according to the wiki.

Rivers are useful to map, fords can be difficult after heavy rain.  A
bridge means you don’t need to worry so much about the rainfall.

Want to know how to get somewhere, routing software works very well except
where two highways don’t quite meet or they cross but without a node.  JOSM
validation will pick these up and that’s really all you need to do basic

Giving feedback, I find correcting the tile and leaving a message
@mappername buildings from imagery should be tagged building=yes by
convention works well as does added 43 buildings.  However if a maperthon
descends on your project and you get swamped with poor mapping then I’m not
above invalidating.  In Ecuador for example I invalidated roughly four or
five tiles for everyone I validated.

Hopefully one or two will read this and decide to do some validation.  We
do need more validators and they do make a big difference to data quality.


Cheerio John
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