Frankie, I think you have mentioned some good examples.
For simple pairs or even small clusters of stops then a stoparea often can be defined by rules – and indeed the systems I am working with in the UK uses such rules to define an “implicit” stoparea – the rules we use are that the commonnames of the stoppoints must be identical, and for a pair of stops they must not be more than 150m apart – or for a cluster the maximum span increases to 250m. Such rules work well in our experience and reduce significantly the number of “explicit” stopareas that need to be created in NaPTAN. These rules work IF the commonname of the stop is identical. If that is not the case, then there are great dangers in assuming proximity alone will give good results – because of natural barriers or other local features that it would be difficult to ensure are understood when trying to create implicit simple stopareas. Stopareas, however, can be much more complex and involve a hierarchy of stopareas to build a complete interchange. For that to work each component stoparea needs to have an explicit reference and therefore needs to be coded explicitly in the NaPTAN data. Only then can you say that stoparea A contains stopareas B, C and D – and interchange is therefore possible between stoppoints in all those stopareas. I think the fundamental question that has not been asked – let alone answered – in the debate so far (at least in those parts of the debate that I have managed to read) is this. Does OSM want to be able to provide data which is a representation of physical reality – in other words it is only interested in stoppoints because they exist on the ground, and not stopareas because they are an abstract concept? Or does OSM want to be able to engage in more detail for public transport and provide data that can be used for functions such as journey planning – in which case it needs either explicit stoparea references throughout, or it needs rules to cover the implicit definition of most stopareas, and explicit relationships to cover those which cannot be defined by rules. If OSM only holds stoppoint data then it represents the physical geography of the situation – and that would be sufficient to allow public transport routes to be added to OSM using those stoppoint references. But as soon as you want to consider aspects of public transport network, then the data will not be sufficient at stoppoint level only. Roger From: Frankie Roberto [mailto:[email protected]] Sent: 24 January 2011 10:06 To: Public transport/transit/shared taxi related topics Subject: Re: [Talk-transit] Summary of Public Transport Proposal Criticism On Mon, Jan 24, 2011 at 9:10 AM, Michał Borsuk <[email protected]> wrote: Am 24.01.2011 09:39, schrieb Roger Slevin: I have not been able to follow the large number of posts on this group in recent weeks - but I can confirm that stopareas are an important part of NaPTAN data in the UK, and are an important aspect of the way that stops data are used in journey planning applications. This is true, but IMHO obsolete. They are used in situations where the routing application does not possess the information on the location of stops. OSM does have that information. Such places can be calculated, instead of being entered by hand. Hi all. I've been following this debate but haven't had time to post as of yet. It seems one of the main bones of contention is that 'stop areas' can be calculated from the existing geographical data, rather than needing to be explicitly stated. I would agree with this if stop areas simply imply 'it is physically possible to interchange between these stops fairly quickly'. However, there's a possible conceptual meaning to 'stop area' which is separate from and non-inferrable from the geographical realities. To take a famous example, I don't think you'd consider Embankment and Charing Cross stations to be part of the same stop area, even though they're very close to each other? On the other hand, some stop areas (Waterloo perhaps) may be huge, even though it may take you more ten minutes to get from one stop to another (even from one tube platform to another). I don't know whether this is intended from the current proposal or not, but I think you could construct a definition of stop areas along the lines of: "a collection of public transport stops, often of differing modes, which are often physically connected by short walkways, often sharing the same name, are advertised as being an interchange on public transport maps and diagrams, and may be treated as a valid interchange by fare structures." - this would seem to me to be a valid use for relations. ?? That said, I'd agree that they're often not really needed in simple cases such as two bus stops on opposite sides of the road. Frankie -- Frankie Roberto Experience Designer, Rattle 0114 2706977 http://www.rattlecentral.com
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