Getting the outer path of a region

I want to get the shapes of an area via overpass that is defined by the first two letters of the postal code. This query:

rel["boundary"="postal_code"][postal_code~"32..."];
out geom;

gets me a number of areas that I want to combine. I am interested in the path of the outer border, i.e. just a single large area instead of the many small ones.

You can see the result on http://overpass-turbo.eu/s/8il .

Is it possible to achieve this via an overpass query only? If not, what might be the most efficient way to provide a JavaScript application with the desired result?

Solution

Overpass API doesn't support this out of the box. After retrieving all relevant postcode relations from Overpass API, you need something like a concave hull post-processing step. As you pointed out in the comment below, one example to accomplish this in Javascript could be http://andriiheonia.github.io/hull/. You might also take a look at gis.stackexchange for alternative approaches (https://gis.stackexchange.com/questions/tagged/concave-hull).

If you just want to tweak the appearance in Overpass Turbo to make the polygons appear like one large area, you should take a look at the MapCSS features included. Here's a small example, which may be used as a starting point: http://overpass-turbo.eu/s/8la

enter image description here

BTW: I'd recommend to limit your query to a certain area/bbox, as your original query also returns some data from Russia.