Avoid overlap of boundaries

hotosm / HDM-CartoCSS

CartoCSS project focused on the Humanitarian Data Model

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Avoid overlap of boundaries #134

Closed yohanboniface closed 9 years ago

yohanboniface commented 11 years ago

screenshot from 2013-07-21 22 36 33

To test:

SELECT DISTINCT ON (geom) ST_AsText( ST_MakeLine(sp,ep) ) as geom
FROM
  (SELECT
    ST_PointN(geom, generate_series(1, ST_NPoints(geom)-1)) as sp,
    ST_PointN(geom, generate_series(2, ST_NPoints(geom)  )) as ep
  FROM
    (SELECT (ST_Dump(ST_Boundary(geom))).geom
     FROM mypolygontable
     ) AS linestrings
  ) AS segments;

From http://support.mapbox.com/discussions/tilemill/885-draw-dashed-borders-of-polygons

yohanboniface commented 11 years ago

I've tried this request:

SELECT DISTINCT ON (way) ST_MakeLine(sp,ep) as way, admin_level FROM (SELECT ST_PointN(way, 
generate_series(1, ST_NPoints(way)-1)) as sp, ST_PointN(way, generate_series(2, ST_NPoints(way)  )) as ep, 
admin_level FROM (SELECT (ST_Dump(ST_Boundary(way))).geom as way, admin_level FROM 
planet_osm_polygon where boundary='administrative' AND admin_level IN ('1', '2', '3', '4', '5', '6', '7', '8', '9', '10') AND 
boundary IS NOT NULL ORDER BY admin_level) AS linestrings ORDER BY admin_level) AS segments

but the result is too uneven, sounds like some pieces have not a strict overlap:

screenshot from 2013-07-26 18 23 16

skorasaurus commented 11 years ago

I haven't verified it, but I assume that this also causes the following at low zoom levels ? Look at the difference between Greenland and Canada/USA for example.

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