# [OSM-talk] maritime borders (was: administrative boundaries and is_in)

Robin Paulson robin.paulson at gmail.com
Sun Jan 13 07:36:36 GMT 2008

```On 12/01/2008, Martijn van Oosterhout <kleptog at gmail.com> wrote:
> On Jan 12, 2008 11:32 AM, Igor Brejc <igor.brejc at gmail.com> wrote:
> > That would be an interesting thing to implement. It would involve
> > creating a union of circles (with radius of 12 NM) and then determining
> > the border of that union. If only I had the time... :)
>
> I thin you'd approach it from the other way. Take a 12nm circle and
> push it against the coastline so it touches at a point. Then "roll" it
> along with the centre tracing a line, forming either an arc where it
> rotates around a point, or a straight line as it slides along an edge.

well, there are two elements to consider:
ways, and points.
ways are easy: as they are drawn a certain direction always (water on
left, is that it?), we just create a set of ways that are 12 nautical
miles to the left of each way.
for points, yes, as igor says it's best to create a circle around each
point, of 12 nautical miles radius.
there must be some (CAD?) library for taking three inputs (two
straight lines, a circle), and working out the necessary start and end
point of the three items, so they form a continuous, smooth (i.e.
tangential) line. then repeat for all point/line combinations

i'll start a wiki page. anyone here have any experience with drawing
libraries? i'm sure we can do this by re-using something that's