feature request #2489
strategy for congruent areas in distribution maps
distribution maps sometimes show areas which are congruent. This occurs because the according areas of different levels (TDWG 4 and 3) are marked with the same distribution status. For example Spain in the map for Sonchus tenerrimus:
Spain appears darker since the area is rendered twice on time per layer and both semitransparent layers overlap.
A sensible strategy is needed to handle these situations.
In this case the
#1 Updated by Andreas Kohlbecker over 5 years ago
- Status changed from New to In Progress
The best solution would be to combine all tdwg layers into one single layer and to have the following four columns in the attribute table (example for northern ireland ):
| tdwg1 | tdwg2 | tdwg3 | tdwg4 |
| 1 | 11 | IRE | IRE-NI |
#4 Updated by Andreas Kohlbecker almost 4 years ago
the approach suggested in comment 1 is not fully sufficient, since the 'areas' that exist of multiple polygons will still have their individual outlines, they are not dissolved or merged.
Further actions are needed to make this work.
see QGis dissolve tool for a possible means
#5 Updated by Andreas Kohlbecker almost 4 years ago
in [#4292#note-10] FranckTheeten mentioned potential problems that could arise from having multiple layers in one shapefile:
"I would recommend to keep them separated. I'm not sure how PostGIS and Geoserver handle overlays, from what I saw today it seems that GeoServer relies on the primary key index of the base layer to handle the z-order at display (the ones with the higher indexes are placed on top of those with lower ), this could prevent displaying a single layer aggregating the 4 zones."
#6 Updated by Andreas Kohlbecker about 3 years ago
- Target version changed from cdm_dataportal - Next Major Release to Release 4.0
- Priority changed from New to Priority14
Yes the render order of the polygons for this layer will for now only be determined by the feature index.
This could be made more deterministic by surrounding each elements in the SLD by its own .
See for reference:
The order of elements in the SLD already follows the order of the elements in the 'ad' map service parameter.
So simply surrounding each element by a should give us the ability to control the render order in merged shape files.
This will make it possible to use a merged TDWG layer with all level (1-4).