TIGER 2017 Pennsylvania county line import?

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TIGER 2017 Pennsylvania county line import?

Albert Pundt-2
I noticed many of the county lines in Pennsylvania are off by quite a bit. I took the county lines from TIGER 2017 and imported them into JOSM, and am ready to begin switching out the existing county lines in OSM. However, I know to discuss before attempting any import, especially one of this scale. What do you guys think?

I should add that with this import, I won't be attempting to add townships to counties that don't already have them, nor will I be improving the accuracy of existing town boundaries in said counties, except where they are adjacent to the county lines.

I do have experience with this type of import, as I added township lines to Lebanon County a few months ago.

Any objections?

—Albert

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Re: TIGER 2017 Pennsylvania county line import?

Frederik Ramm
Hi,

On 01/24/2018 12:46 AM, Albert Pundt wrote:
> I noticed many of the county lines in Pennsylvania are off by quite a
> bit. I took the county lines from TIGER 2017 and imported them into
> JOSM, and am ready to begin switching out the existing county lines

Do you mean you'll keep the relations intact and just replace the member
ways, or do you intend to delete the relations wholesale and introduce
new ones?

Where county boundaries are shared "upwards" by the state boundary, or
"downwards" by a city boundary, will you ensure that these links are
kept? County boundaries often don't exist in a vacuum and hence when the
county bondary changes, the city/state boundaries need to change too,
else you'll end up with cities straddling a county border or counties
straddling a state border...

Depending on what exactly you're planning to do, the JOSM "utilsplugin2"
function "replace geometry" might be useful; it would try to keep the
existing objects in OSM and just refine their geometry, rather than
deleting and re-creating stuff.

Bye
Frederik

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Frederik Ramm  ##  eMail [hidden email]  ##  N49°00'09" E008°23'33"

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Re: TIGER 2017 Pennsylvania county line import?

Albert Pundt-2
> I noticed many of the county lines in Pennsylvania are off by quite a
> bit. I took the county lines from TIGER 2017 and imported them into
JOSM, and am ready to begin switching out the existing county lines

> Do you mean you'll keep the relations intact and just replace the member
> ways, or do you intend to delete the relations wholesale and introduce
> new ones?

> Where county boundaries are shared "upwards" by the state boundary, or
> "downwards" by a city boundary, will you ensure that these links are
> kept? County boundaries often don't exist in a vacuum and hence when the
> county bondary changes, the city/state boundaries need to change too,
> else you'll end up with cities straddling a county border or counties
> straddling a state border...

> Depending on what exactly you're planning to do, the JOSM "utilsplugin2"
> function "replace geometry" might be useful; it would try to keep the
> existing objects in OSM and just refine their geometry, rather than
> deleting and re-creating stuff.

I certainly don't intend to delete and recreate any relations for no reason. Links with other boundary types will of course also be kept. The state boundary itself will likely be redone as well to match the more accurate newer TIGER data, though along the Mason-Dixon Line the border is defined by boundary stones which are already mapped, so I won't touch that part.

I'll definitely take a look at that plugin, it could help quite a bit. I also know not to delete member ways either in order to preserve history. What I've been doing as I edit roads is reduce the original way to a short segment, merge that in with the new way, and then just delete the last node to fully roll the old history in with the new way. If that plugin removes the need to do this for every single boundary way, that's great!

—Albert

On Tue, Jan 23, 2018 at 7:31 PM, Frederik Ramm <[hidden email]> wrote:
Hi,

On 01/24/2018 12:46 AM, Albert Pundt wrote:
> I noticed many of the county lines in Pennsylvania are off by quite a
> bit. I took the county lines from TIGER 2017 and imported them into
> JOSM, and am ready to begin switching out the existing county lines

Do you mean you'll keep the relations intact and just replace the member
ways, or do you intend to delete the relations wholesale and introduce
new ones?

Where county boundaries are shared "upwards" by the state boundary, or
"downwards" by a city boundary, will you ensure that these links are
kept? County boundaries often don't exist in a vacuum and hence when the
county bondary changes, the city/state boundaries need to change too,
else you'll end up with cities straddling a county border or counties
straddling a state border...

Depending on what exactly you're planning to do, the JOSM "utilsplugin2"
function "replace geometry" might be useful; it would try to keep the
existing objects in OSM and just refine their geometry, rather than
deleting and re-creating stuff.

Bye
Frederik

--
Frederik Ramm  ##  eMail [hidden email]  ##  N49°00'09" E008°23'33"

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Re: TIGER 2017 Pennsylvania county line import?

Mike N.
On 1/23/2018 8:29 PM, Albert Pundt wrote:
> I certainly don't intend to delete and recreate any relations for no
> reason. Links with other boundary types will of course also be kept. The
> state boundary itself will likely be redone as well to match the more
> accurate newer TIGER data, though along the Mason-Dixon Line the border
> is defined by boundary stones which are already mapped, so I won't touch
> that part.

   I second the "Replace Geometry" tool for this type of update.  I was
able to create a new way matching the length of the old and then replace
geometry and join the ends.   One thing to check carefully is for any
other object which has been attached to the old boundary.  That got me
where 2 roads terminated on the boundary and each other; that point
would be lifted and cause a gap in roads for example.

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