[talk-ch] Semantics through abstraction (Re: Pls, don't delete sidewalks, visual impaired people might use them)
nzaraosm at gmail.com
Fri Aug 25 09:27:44 CEST 2017
I support these arguments.
Am 25.08.2017 um 00:08 schrieb Raphael Das Gupta (das-g):
> marc bring up good and valid points.
> On 24.08.2017 23:12, marc marc wrote:
>> 3) It is only afterwards that one can draw the sidewalks separately
>> without sending the people into a dangerous situation.
> In what I assumed up today to be the consensus, there are two cases
> when sidewalks should already now be drawn separately:
> 1. (as already mentioned) when separated from the street by space
> (i.e., not actually laterally connected to the street)
> 2. when separated from the street by a barrier (e.g. as seen here
> <https://www.openstreetcam.org/details/8505/3981> on the
> right-hand side)
> In all other cases, for the time being, the presence (or absence) of
> sidewalks should indeed be represented by additional tags on the
> street's way rather than dedicated ways for the sidewalks, and I'm not
> even sure whether we should pursue
>> 1) have a tag or relation with a meaning "This sidewalk is separated for
>> geographical precision, but for routing, it is permanently connected
>> to the road".
>> 2) Have at least one routing algorithm that can use it.
> as that would complicate things further for both mappers and data
> users. (I do agree though, that if we /were/ to map all sidewalks
> separately, whether separated or not, these steps would have to be
> taken first.)
> Maps (and map data) must abstract (and therefore, to some degree,
> simplify, aggregate and interpret) reality. It must do so, not (or at
> least not primarily) as a means to save data size and mapping effort,
> but to be adequately useful at all. Taking it to the extreme, to make
> that point obvious: The information "there is, here on this street, a
> rectangular yellow paint application on the ground, and next to it
> another one and another one and several more"* is much less useful
> than the information "here on this street, there's a marked pedestrian
> For sidewalks this might be less obvious, but there's an important
> semantic difference between "there are a street and a sidewalk next to
> each other, with unknown lateral relation to each other" and "there's
> a street with a sidewalk at the right-hand side", because in the
> latter case, you can (even though you might not be allowed to) walk
> from the sidewalk onto the street or (even though you might not be
> allowed to) park a car on the sideway or let someone unboard the car
> right onto the sidewalk or let them board the car right from the
> sidewalk. Or you might inadvertently trip and step onto the street.
> When they are physically separated by space or a barrier, this isn't
> usually possible and thus this warrants mapping the lateral adjacent
> and the physically separated case so differently.
> Given tools and maps that know about and use this convention to
> interpret the data (and given data that actually sticks to the
> convention) this will help blind or otherwise visually impaired people
> just as much (or even more) than fully seeing-capable ones.
> *remember the cantonal GIS that had street ground markings mapped with
> the actual outlines of the colored area (i.e., dashed lines as series
> of rectangles, arrows as 9-or-more-vertice polygons, "STOP" markings
> as vectorization of the actual letters "S", "T", "O" and "P", etc.)
> instead of their semantics in traffic? While very accurate, that
> probably isn't useful, unless the road traffic department had planned
> to renew those markings with a street-wide inkjet printer vehicle or
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