[Talk-transit] NaPTAN bus stop database import - some more observations

Brian Prangle bprangle at googlemail.com
Wed Apr 1 13:41:00 BST 2009


Some more views and observations  on the NaPTAN data import in Birmingham:

1.       It serves as a great QA on OSM data and shows that in the City
Centre where we have not been able to get decent GPS traces more accuracy is
needed so the potential of obtaining aerial photography is great.

2.        It’s a great impetus to resurvey streets where earlier work
(potentially inaccurate from NPE tracing, older GPS devices, less points
collected,  inexperience, not realising that roads have a width greater than
the rendered line so placing bus stops too close to the road etc.) can be
improved.

3.       It’s also a great impetus to improve practice on surveying bus
stops and be much more precise and comprehensive – also a stimulus to edit
all those old bus stops where we placed them as a node on the way rather
than to the side of ways which is our current practice.

4.       QA works both ways and our surveys should help to improve NaPTAN
data.

5.       As an exercise(excuse the pun!) I cycled from Acocks Green to
Moseley and back this morning along the No 1 bus route and surveyed 47 bus
stops each time standing at the pole(leaning against it – you can’t get
closer than that!)  or underneath the plate at a shelter:  4 bus stops
coincided within 3-4 m; 17 were “good enough” coinciding <8-10m. That’s
approx 45%. The rest were out by anything up to 90m or were just missing.

6.       I think either the pole where there is no shelter or the bus stop
plate at a shelter should be what we survey – that’s where the
identification of what we survey is located

7.       Where a physical stop on one side of the road doubles up for one on
the other side also – I think we’re OK by surveying and tagging the physical
one with Andy’s suggestion of a tag opposite=yes. The NaPTAN untagged node
on the other side can be left in place to indicate the  logical
relationship.

8.       I like the idea of tagging where the bus stop is set back in a
“lay-by” from the road which might account for some NaPTAN nodes being some
distance from the road

9.       For our purposes “good enough” is probably sufficient rather than
precise positional detail – I’m of the view that as long the bus stop has
more or less the right relationships to its surroundings then that’s OK.

10.   Surprised that there is no data for either the closed Digbeth Coach
Station which is being rebuilt or the temporary replacement nearby. I
thought we were importing off-street bus stops? Perhaps the NaPTAN data
doesn’t exist?

11.   Can’t find any nodes for  taxi ranks – not imported or doesn’t exist
for Birmingham or I’m not looking hard enough?

12.   For the few nodes where I’ve estimated the fit between OSM and NaPTAN
to be “good enough” I’ve merged the nodes deleting the unverified tag
and  editing
source tag to v=naptan_import;survey

13.   Verifying the data is going to be a long, slow process with a lot of
resurveying needed.
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