On Thu, Sep 25, 2008 at 12:53 PM, Dave Stubbs <[EMAIL PROTECTED]>wrote:
> On Thu, Sep 25, 2008 at 11:47 AM, 80n <[EMAIL PROTECTED]> wrote: > > This is an interesting topic which is well worth discussion, but to > return > > to the original question for a moment. The issue is that mapnik is not > > capable of rendering a way that is both a path and an area. The example > > given was highway=service, amenity=parking. > > > > Regardless of whether people are centerlineists or not, there are always > > going to be mappers who will tag ways this way. We have a free form > tagging > > scheme so we cannot prohibit such things. For example, a way tagged as > > highway=waterway, power=line (two linear tags) might be unusual (water > and > > electricity generally don't mix ;) but we cannot disallow it. > > Umm... I don't like that argument. > > Saying we have a free form tagging scheme, and saying all the > renderers should just cope with absolutely anything someone happens to > have done are two very different things. > We may not be able to "disallow" something, but we can sure as hell > disagree with it and refuse to support it in a particular tool. > > Just because everything is "allowed" does not mean there is no such > thing as "wrong" either, it just means our mechanisms for coping with > it are different. > > > > > > So, if a way is tagged as highway=service to describe a road, but also > > amenity=parking to indicate that the road *"is part of the car park and > > defines its boundaries"* then that's the way it is. > > > > Suggesting that the data be changed to accommodate the deficiency of a > > particular renderer is very much a case of mapping for the renderer. > This > > is a principle that is important to uphold. Fix the renderer not the > data. > > > And this is the point -- it's not a deficiency... as far as I'm > concerned the car park has been incorrectly modelled. There is no > sense in tagging a feature as both a line and an area... that way > madness lies. You're proposing that a field with a hedge around it should be tagged as two separate ways that share the same set of nodes right? A single object tagged with landuse=field, border=hedge seems pretty reasonable and intuitive to me. Where's the madness in this? In this case a renderer might choose to render the field as an area or the border as a line or, indeed, both. Sometimes it can be the renderer that needs to decide whether something is rendered as an area or a line or even a point. A roundabout being a good example where at some low zoom level it could be an icon, at another it's a filled in blob (an area), and at a high zoom level its a road with a hole in the middle. 80n > And tagging a way/area with more than one feature can be > just confusing. One feature per object is an entirely sensible rule > that people are of course free to ignore... just don't expect anything > to ever work if people make a regular habit out of it. The problem is > that all sense of predictability has just been thrown out... does this > represent a road around a car park, a road in a car park, an area of > service road you can park on, or a centre line of a service road you > can park on? > > Dave >
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