Export Coast Line in hi quality

General talk
1

Ciao!

i’ve tried to download the shapefile of CoastLine: shoreline_300.tar.bz3 but is seems to be a “low resolution”…

I’m expecting the same quality of the deepest zoom of OSM? or i’m wrong?
Which is the best download in order to have the best quality for the “so called” coast line (the one that is tagged as natural=coastline i mean!)

Thanks thanks and again thanks
Alberto Gorni

2

Have you already tried all information at http://wiki.openstreetmap.org/wiki/Coastline ?

3

i’ve already downloaded this:

http://tile.openstreetmap.org/shoreline_300.tar.bz2

but i’ve found that is in Mercatore projection
and that is a poor quality… (at least for my scope)

Now i’m trying to load the http://tile.openstreetmap.org/processed_p.tar.bz2
should be this one the file i’ve to try?? it seems that mapnik renderer use this for the hi zoom levels?? is it true?

A question now is… does it use Mercatore projecto as well??

Thanks
Alberto

4

Yes, processed_p has the full resolution, and is in the 900913 projection.

5

And projection does not matter, they are vector data and they can be re-projected to any suitable projection with, for example, ogr2ogr without any loss in accuracy.

6

Yea i know about the projection… i’ll use too the 900913 so it’s better for me to have data already projected… then i plan to insert into sql 2008 this data that will be used to render coast line…

anyway i’ve tryed to import using a tool called Shape2Sql.exe from “sql spatial tool” but it tell me that there is some “error” in the polygons:

The Polygon in input is not valid because the ring does not have enought distinct points. Each ring of a polygon must contain at least three distinc points.

this happens for the geometry with attributes: tile_x_: 13 tile_y:4

I’ll investigate…

7

…and what about if i would like to export even the entire state boundaries? in full resolution and then what i can do to obtain a “low res” version like the precalculated “shoreline 300”??

8

You will see that there are some features which could be called as A-B-A polygons. It means that they have been defined as polygons and they have three vertises but only two distinct points, A and B. The polygon starts from A, goes to B and then comes back to A. On a map it looks like a short line. They are not real polygons, for example they have zero areas, and I believe that most systems consider those are topologically invalid but Mapnik does not care.

9

Mhmm… exactly! may it be! but i don’t know if is it a real valid geometry even for SQL 2008 too!
why this short line is not represented as linestring instead of polygon?

…even if… in the end i’m asking myself the necessity of this type of geometry when describing a coast line?

thanks for reply!