[talk-ph] GNS town and city import (was: Hi Guys and Gals, Open Street Map)

[maning sambale]

excellent work!  Just for the record,  I have edited the names (not
the location) of some municipalities in Mindanao.  Most Municipalities
have the name "Municipality of X".  I just remove the "Municipality
of".

Maybe we can check the history for moved nodes. Or just don't import
in well-mapped areas.  Mike Collinson (who made the import) might help
you merge the data as well.

On Thu, Jan 22, 2009 at 3:05 PM, Axel Kollmorgen <axel at kollmorgen.net> wrote:
> On 19.01.2009 11:50, Eugene Alvin Villar wrote:
>> I think the place points for the towns and cities were imported from
>> the GeoNet Name Server. See this wiki page:
>>
>> http://wiki.openstreetmap.org/wiki/WikiProject_Philippines/Data_import#Geonet_Name_Server
>>
>> And it seems there are indeed errors. One town in the province of
>> Compostela Valley is placed out in the Philippine Sea!
>
> this is because GNS specifies towns and cities (Feature Designation Code
> (DGS) == ADM2 (second-order administrative division)) with a low 1 to 2
> digits after the comma precision only. which makes sense, as these
> entities can be quite big.
>
> there are also much exacter (3 to 5 digit precision) coordinates of all
> these towns and cities in GNS, the ones with DGS == PPL, populated
> place. for example, for maasin in southern leyte:
>
> ADM2:   10.2, 124.85
> PPL:    10.133611, 124.844722
>
> unfortunately, there is no easy way to relate the place with the exact
> coordinates to the administrative division. which i guess is why the
> import used the low precision coordinates and we got towns in the
> Philippine Sea and coastal towns on mountain ranges now.
>
> there might be some way, though. i've been fiddling around with this for
> some hours now and got some results that don't look too bad. my basic
> idea: get the name and some other characteristics (province, jog) of
> ADM2 and find the PPL entry with the same name and characteristics.
>
> there are some problems with this approach: ADM2 and PPL must have the
> same name (doesn't work for "Ormoc City"/"Ormoc"), sometimes there are
> more than 1 PPL with the same name and characteristics as ADM2 ("San
> Miguel"), sometimes the PPL coordinates are not of better precision, ...
> nonetheless, with some tweaking, i got precise coordinates for 1271
> towns and cities, or 78% of the "136 cities, 1,495 municipalities" [1]
> of the philippines.
>
> for a visual comparision of the old import and my results, i uploaded 2
> josm screenshots of leyte with landsat background [2]. first with the
> old towns and cities, then with the better precision. note how the
> coastal towns align nicely with the coastline in the second image.
>
> comments? any interest in redoing the import like this?
>
> ax
>
> p.s. does anyone know of a way to automatically find all towns and
> cities that have been edited / relocated after the initial import? these
>  towns wouldn't have to be reimported.
>
> [1]
> http://en.wikipedia.org/wiki/List_of_cities_and_municipalities_in_the_Philippines
> [2] http://picasaweb.google.com/axkosm/gns
>
>
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-- 
cheers,
maning
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