Conversion of LineString to Polygon

Question

I am using overpass api to get the OpenStreetMap data. I have a following query:

[out:json][timeout:25];
// gather results
(
  // query part for: “"Land Use"”
  way["landuse"](around:1000, 49.058008 , 2.275715);

);
// print results
out body;
>;
out skel qt;

Try it out here: http://overpass-turbo.eu/s/mOu

The problem is that it always returns LineString instead of Polygons. I would like to convert LineString to Polygon in order to use this data for intersection analysis of different Polygons. Is there a way to convert LineString to Polygon(e.g. with geoJSON library ), or should I change my query for this?

Thanks you in advance

Answer 1

1

OSM only knows nodes, ways and relations. Ways can be closed in which case they form an area. So when you export a landuse via OverPass, you get a closed way. Isn't a polygon just another word for closed way ?

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answered 19 Feb '17, 19:54

escada
19.0k●16●166●302
accept rate: 21%

Thanks a lot for you answer. Indeed, it is a polygon,when it is a closed way and when the line does not intersect itself. Otherwise it is a more then one polygon. I would like to compute the area of these polygons. The problem is that I am not sure that it is possible, unless it is a polygon. I am using python shapely or gdal for this. So I started to think about conversion of the strngline to polygon.

(19 Feb '17, 20:31) tivalex

1

Since OSM does not know polygons, in which programming language are you working ? To find out whether an OSM way is a closed way, you could test whether the first and last point are the same, not ? So it is up to your processing software to determine whether a way is closed and if it is closed, calculate the area.

(20 Feb '17, 06:34) escada

It is totally make sense. However, I tought that there is some kind of a way to define a shape in the query. Or automatically convert Linestring to Polygon with help of some library. And I query only type of data that should be a polygon eg. landuse or building. Like described here: https://wiki.openstreetmap.org/wiki/Overpass_turbo/Polygon_Features Most likely I don't need to check whether it is a polygon or not. Asking to your question: I use Python for this.

(20 Feb '17, 08:07) tivalex

Conversion of LineString to Polygon

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