[API-users] Clipping occurrence data to a country

Adriaan van Os adriaan at adriaan.biz
Thu Jan 10 11:10:09 CET 2019

Matthew Blissett wrote:

> For the other approach, I don't have EPSG:3575-format vector tiles with 
> country borders, but in any case it's difficult to work with vector 
> tiles for any further processing — if you wanted a polygon, you'd need 
> to reconstruct it from the lines which are cut off at the edges of the 
> tiles. I recommend you use a different source of map data, e.g. from 
> http://www.naturalearthdata.com/ . Many GIS libraries (including 
> Javascript ones for display) should be able to work with that data, for 
> example in GeoJSON format: 

With some programming, the poly-edge cutting problem can be solved. Besides, on large-scale maps 
with small polys, I find cutting the poly edges really improves the looks of the map. Also, one 
could use the country borders to highlight (e.g.) a specific country on the background-map before 
overlaying the occurrence polys. So, I do suggest adding "&country=" to the GBIF background-map 
tile API.

> https://github.com/nvkelso/natural-earth-vector/tree/master/geojson (if 
> 10m resolution is sufficient).

Thanks !

The Natural Earth Admin0 data sets 
<https://www.naturalearthdata.com/downloads/50m-cultural-vectors/> are what I need. Best of all, it 
can be loaded into QGiS and converts perfectly well to EGCS:3575. There is not much on the internet 
(that I could find) for converting to EGCS:3575. I have only located QGiS, OpenLayers (apparently) 
and Leaflet (Proj4Leaflet c.s.). And GBIF, of course.

The advantage of EGCS:3575 is that it is an equal area projection 
<https://en.wikipedia.org/wiki/Lambert_azimuthal_equal-area_projection>, unlike EPSG:3857 Web 
Mercator. I don't like Web Mercator distortions. I guess EPSG:3857 became polular when Google 
started to use it, thinking that people will be confused when the line pointing North isn't 
vertical. God should have made the earth a cube for that purpose ? Well, that causes some problems 
at the edges when travelling ....

I will investigate the &country=NL issue further and reply seperately.


Adriaan van Os

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