[API-users] Clipping occurrence data to a country

Adriaan van Os adriaan at adriaan.biz
Fri Jan 11 12:56:37 CET 2019

Matthew Blissett wrote:
> I've made an issue and a live demo: 
> https://github.com/gbif/maps/issues/29 (using vector tile points, as the 
> polygon maps are generate from the point sources, and the raster tiles 
> from the vector ones).

The Dutch data are peculiar in that a system is used in the Netherlands that counts (not just 
moths) in each 5x5 km square. That has some interesting effects on GBIF maps:

1. The GBIF polygon maps from such data show a Moiré pattern, caused by two rasters interfering 
(GBIF polygons and the Dutch 5x5 squares) unless the polygon size is carefully choosen.

2. The point maps don't show a "natural distribution" in the Netherlands as can be seen in this 
example <http://lepidoptera.online/gbif/aglais-io-hokjesmentaliteit.png>

3. Apparently, the Dutch data have an offset and must be shifted to the North-East to align. I 
don't know if this is a GBIF or Dutch data problem. Nor do I know if it is the center of the 5x5km 
squares that is entered as GBIF map position.


Adriaan van Os

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