[OSM-dev] About the geographic data in a .osm file

[Peter Wendorff]

Just to avoid confusions: The Geofabrik extracts does not cut along the
borders exactly, too.
They should be better (I guess), but not exact.
Exact splitting is much more expensive in terms of time and memory than
splitting a rough bounding polygon. That polygon should contain the
whole country, but may contain additional areas to reduce complexity.

And - of course: As far as I know none of the available extract services
splits ways or areas (except multipolygons probably) when exporting, so
if a way crosses the border, it's usually contained completely in the
extract.

regards
Peter

Am 24.05.2013 23:16, schrieb Vince Berubey:
> Thanks Toby,you answered exactly what I was trying to understand.
> - I do understand why i'm getting blank tiles.- I wanted to know why there is data outside of delaware.
> I do understand know.
> 
> Date: Fri, 24 May 2013 16:12:33 -0500
> Subject: Re: [OSM-dev] About the geographic data in a .osm file
> From: toby.murray at gmail.com
> To: screams_3 at hotmail.com
> CC: dev at openstreetmap.org
> 
> 
> First of all, did you notice that the cloudmade extracts are over a year old? I would suggest looking at geofabrik for up to date extracts:http://download.geofabrik.de/north-america.html
> 
> As for your tiles quesion, I'm not quite sure what you mean. Are you asking why there is any data outside of Delaware? Or why you are getting blank tiles where you don't have any data?
> 
> The cloudmade extracts never were too accurate on the state borders. When I first downloaded Kansas they were missing the north border by a couple of miles and had extra on the south. So it doesn't surprise me that the cloudmade extract has extra data in it.
> 
> As for tile generation, the tile rendering process doesn't care about where you do/don't have data. It just renders the tiles you tell it to render. If there happens to be no data in that area then the tile will be blank.
> 
> Toby
> 
> 
> On Fri, May 24, 2013 at 3:08 PM, Vince Berubey <screams_3 at hotmail.com> wrote:
> 
> 
> 
> 
> I have downloaded "delaware.osm.bz2 " http://downloads.cloudmade.com/americas/northern_america/united_states/delaware#downloads_breadcrumbs
> 
> The boundary box I used when I generated my tiles from Generated_tyles.py  were a little bit bigger than the Delaware region.
> What I don't understand is why I was able to generate tiles that were in my boundary box, but outside the Delaware area.
> 
> So, the .osm file does not exactly contain only the geographic data from the region that you have downladed?
> Please look at this file, the red marks are the Delaware borders. I have a lot of tiles generated outside of these borders:
> 
> http://postimg.org/image/ogwbjz5ln/
> Thank you for any explanation about it.
> Best regards.
> 
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