[OSM-talk] Slippy map - Mapnik layer UK coastlines

Artem Pavlenko artem at mapnik.org
Fri Mar 23 17:56:00 GMT 2007


On 23 Mar 2007, at 17:10, David Groom wrote:

> ----- Original Message -----
> From: Artem Pavlenko
> To: David Groom
> Cc: talk at openstreetmap.org
> Sent: Friday, March 23, 2007 1:48 PM
> Subject: Re: [OSM-talk] Slippy map - Mapnik layer UK coastlines
>
> Hi David,
>
> On 23 Mar 2007, at 11:48, David Groom wrote:
>
>> It seems that the UK coastline is beginning to render better in  
>> the Mapnik
>> layer of the slippy map (it's a solid blue fill, rather than the  
>> odd shaped
>> grey polygons).
>>
>> However it does appear that the source for the coastline might be  
>> a rather
>> out of date planet file.
>>
>> In some places, eg
>> http://www.openstreetmap.org/index.html? 
>> lat=50.85383936185782&lon=-1.315713476905844&zoom=15
>> ,there is an exact correlation between coastline which is shown in  
>> the
>> Mapnik and Osmarender layers.
>>
>> In other places eg ,
>> http://www.openstreetmap.org/index.html? 
>> lat=50.81094579389664&lon=-0.09869895092239864&zoom=15
>> ,the coastline outline in the Osmarender layer seems to be much  
>> more recent
>> than the Mapnik layer.
>>
>
> For most of the world I was using original shoreline data, hence  
> it's not as smooth as it should. Polygons are only available for  
> England and Wales, the rest gets blue shoreline lines.  To have  
> proper polygons for the whole planet :
>
> 1. We need to agree that storing countries boundaries as polygons  
> is way forward.
>
> 2. We have to decide if storing these polygons in main OSM database  
> is a good idea or not. I personally think it'll be better to store  
> them separately.
>
> 3. Start creating polygons. I have all the tools and I'm happy to  
> help anyone, but it is a big task which requires community  
> participation.
>  On the other hand, If one person capable of fixing most of the UK  
> coastline it should be peanuts for OSM as a whole. If you want to  
> see nice blue sea and land just do it, don't wait!
>
>  Cheers,
> Artem
>
>> David
>>
>>
>>
>> _______________________________________________
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>> http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
>>
>
> Artem Pavlenko
> http://mapnik.org
>
>
>
> My original query remains, since both areas I was referring to are  
> in the UK, about 70km away from each other.
For Southampton area I used coast-line from OSM and Brighton uses  
original shore-line data.  Polygons are tiles by 100x100km.

> I  can see advantages and disadvantages to storing polygons in the  
> main OSM database.  One disadvantage I guess is it will  
> dramatically increase the amount of data in the database, but I  
> presume it would have the advantage that the polygons can be  
> edited / amended using the usual OSM tools, so that alterations  
> could be made by people with local knowledge
Agree. But if we want to edit boundaries we need to improve OSM tools  
to be able to handle geometries such as Polygons, basic topology  
checks etc.  All libraries are out there - JTS for Java and GEOS for c 
++.  And of course data model thingy :) . There is no official way to  
store Polygons with loops (holes) with current data model AFAIK.

> Once 1) & 2) are agreed I'd be happy to assist if I can.
Me too!

Cheers
Artem

> David
>
> _______________________________________________
> talk mailing list
> talk at openstreetmap.org
> http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk

Artem Pavlenko
http://mapnik.org



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