[talk-ch] Semantics through abstraction (Re: Pls, don't delete sidewalks, visual impaired people might use them)

Nzara 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 
> crossing".
>
> 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.
>
> Regards,
> Raphael
>
> *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 
> something.
>
>
>
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