[OSM-talk] tagging and rendering

[elvin ibbotson]

On 9 May 2008, at 12:21, Dave Stubbs wrote:

>
> The mapping to numbers doesn't gain us anything. It doesn't let us do
> anything we can't already do, or make it any easier as far as I can
> see.

If the database, which is accessed by programmers, was numerically  
based, it would be be more amenable to algorithmic logic. At the  
simplest level, selecting elements with values above/below certain  
levels. The numbers would of course have to follow some logical  
pattern. Similar procedures using the current tags involve clumsier  
code like 'motorway OR trunk OR primary' and, if users are actually  
typing these words in (rather than selecting from human-friendly  
menus presented by the editor) a typo such as 'secodnary' cold  
corrupt the database and prevent the feature being seen by map  
viewers or routing engines for example.

>
> I think you were actually suggesting something like "type=11" -- where
> 10-20 means roads, 30-40 could mean railways etc. But as far as this
> argument goes it doesn't really make much difference, other than
> leaving us with a massive allocation problem which has been neatly
> sidestepped by using free-form tagging.

Yes free-form tagging avoids having to decide on a pattern and allows  
for open-ended evolution, but it doesn't work if it's completely free- 
form. I could describe many roads around here as 'highway=country  
lane" but would they get rendered? The fact that there are tagging  
recommendations acknowledges that anarchy would not work. But a data  
structure would have to allow change and evolution (at the simplest  
level, leaving spare numbers for future use) and this is a challenge.

>
> Indeed point missed again.
> We DON'T DO (sorry Richard) highway=red. We do highway=primary and you
> can make that any colour you like... same as you can do with
> highway=13/type=13 -- it makes no difference is my point. Numbering
> the highways won't help.
>

Now I'm confused. I'm not suggesting numbers to avoid red highways  
for goodness' sake!

>>
> It could yes. There are a couple of issues with this mostly to do with
> actually maintaining the style sheets and providing the processing
> power/disk space.
>

Moore's Law should take care of those :-)

>>
>>
>> No problemo! Special viewers like the cycle map would simply apply  
>> their own
>> filters. And with well-structured data a map viewer could even  
>> have settings
>> (eg. cycle routes on/off) allowing it to be customised by the  
>> user, making a
>> proliferation of specialist viewers unnecessary.
>>
>
> Hmm.. yes, maybe. But the point of your e-mail was essentially
> numbering everything, and that really doesn't help us with this goal.
>

It's just that numbers are easier for programmers (see above). Users  
would never see them. They would see words in their own language and  
the viewer/editor would map words to numbers.

elvin

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