How to show *just* what's within an administrative boundary?

General talk
1

As a background image for a presentation, I’d like to be able to show a map of a particular area within some administrative boundary, but with just white space beyond it, i.e. as though I have cut the region out of a map.

I’ve done it once or twice by simple taking a screenshot of the map with the whole area visible, and then painting over the parts beyond the boundary in white with an image editor, but it’s pretty tedious to do.

Can anyone suggest an easy way to obtain a cut-out map of an administrative area, whether it’s “Norway” or “Bolton Borough Council” or “Kansas” or whatever?

Thanks in advance.

2

One way to do this is to get the already cut out OSM data from
geofabrik.de and to render with Kosmos.

Chris

[1] http://download.geofabrik.de/osm/
[2] http://wiki.openstreetmap.org/wiki/Kosmos

3

How about exporting as an SVG? I don’t know exactly how, but it shouldn’t be hard to cut out everything outside the border.

4

You can use Osmosis to extract a polygon from an osm file. Instructions here: http://wiki.openstreetmap.org/wiki/Osmosis/Polygon_Filter_File_Format
You could then render that with Kosmos etc.

5

Thanks for the suggestions. I’ve never used Kosmos, but I’m going to dust of my old steam-powered XP machine and see if I can get it up and running. (Don’t suppose there’s a cross-platform/web-based application for doing similar things, is there?)

6

Think than you mean: You can use Osmosis to extract all data within a polygon given an osm file and a polygon file.

I immedeately had a look at that page to see how its done. Then I encountered some things I don’t understand. From the wiki:
The polygon section name may optionally be prefixed with “!” to subtract the polygon. The section(s) containing the larger area from which to subtract should be listed first. All the polygon sections are combined together to create the final filter area."

First I do not understand what “subtract a section” means. To see what was ment (there is a !2 in the australia_v polygon data exemple), I displayed it on the map. There are two small areas. One a 100 km south of Melbourne. The other a 500 km to the west. Is this just an unlucky subtraction example? Or what do I mis?

Next problem:

  • Osmosis bounding-polygon task*
  • Example command to extract a polygon using such a file (if was named country2pts.txt) :*
    For me a confusing description. When Osmosis starts it’s ‘bounding-polygon task’ there should already be a polygon (you can extract that fom osm data too. But you should already have done that.). After that Osmosis can use the polygon file to extract all data within that polygon from an osm file.

As one can extract both polygons and data within polygons (the latter also called splitting) from osm files confusion lays ahead. I think the wiki is the first place to avoid that.

Last problem:

  • In case you would like to use a Polygon file of an area with a certain buffer distance*

It is unclear to me what is ment with a buffer distance. I think adding one sentence could resolve that.