On 06/10/18 21:34, Andrew Harvey wrote:
Thanks for raising that. I'd seen some boundaries in WA defined in
legislation as, follow this road, then that road etc. but I think that
was for school zones. So the LGA and Suburb/Localities are defined by
the cadastral plans then?
I hear the points and see there is consensus to not reuse existing
roads, rivers in the admin boundaries, so I support that approach.
What about admin boundaries that border the coastline? Should they
share the existing coastline or not?
OSM has defined the 'coast line' as the high tide mark as that is easier to
pick than the low or mid tide marks.
It is probable that the admin boundaries use the low tide mark?
Do a sample comparison?
That does simplify the import, as there is much less manual effort needed.
I guess what we need now is an OSM XML file with both the
Suburb/Localities and LGA boundaries together with shared ways (as
many ways are in common). I'll see what I can do to put this together,
is anyone else working on this too?
On Sat, 6 Oct 2018 at 20:53, cleary <[email protected]> wrote:
In regard to administrative boundaries being attached to other features such as
waterways and roads, I think it is a trade-off between accuracy and convenience.
I am most familiar with NSW. Boundaries are not "defined" by words but rather by
surveyors' charts. The surveyors may often have been directed to use waterways, roads, mountain
ridges and similar features for their surveys. However the waterways and roads have sometimes/often
moved but the boundaries have not. Words are sometimes used to describe boundaries such as
"it follows the river and then goes south along the main road ... " Such a description is
approximate and is near enough for many purposes, especially if one's area of interest is well
within the boundaries. However it may not be sufficiently precise if one is concerned with
particular locations close to the boundaries.
Examples in NSW that might be considered include the boundary on the Murray
River west of Tocumwal, the Lachlan River east of Cobb Highway, Willandra Creek
south of Roto, Bogan River at Girilambone. If the boundaries were attached to
the respective waterways, either the boundaries or the waterways would be
incorrect. Where boundaries are mapped on rivers or roads, mappers may re-align
the river or road as changes occur and the administraitve boundary becomes
distorted, sometimes only slightly but usually increasingly significant over
time. Alternatively we could map the waterway or road using the administrative
boundary data (as some mappers have done in the past) and ignore the satellite
imagery and GPS data but this affects the accuracy of the location of the
waterway or road.
While I will accept the community's group decision, personally I think accuracy
is to be valued over convenience. I strongly advocate for accuracy by mapping
administrative boundaries separate from other features on the map, even if they
are nearby.
The decision in regard to the above issue will affect use of a source tag for
the boundary. If the boundary is an approximation and attached to waterways or
roads then it would be incorrect to use a boundary source tag, However if
boundaries are mapped separately and accurately, then we should record the
source of the boundary data. While I would suggest adding the source tag to the
relation for the administrative boundary, it might also be added to the way if
there is any need to specify the source for the way e.g. if using the
administrative boundary for the geography of a river, then also give the source
of the boundary data as the source for the waterway.
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