Installed packages
holoviews 1.14.4, geoviews 1.9.1., matplotlib 3.4.2.
What I'm trying to do
I am trying to apply simple per-feature styles using GeoViews and the matplolib backend. I cannot figure out how to apply different edgecolor= parameters to different gv.Polygons elements in the same overlay. For some reason, they're always lightblue...
Similarly, facecolor= seems to have no effect.
Reproducible code sample
This uses a very small sample of the full dataset.
import pandas as pd
import geopandas as gpd
import geoviews as gv
from geoviews import opts
# loading both extensions as the full script calls for user input
# to choose between an interactive or static output
gv.extension('bokeh', 'matplotlib')
d1 = {'use': {0: 'Residential', 1: 'Residential'},
'geometry': {0: 'POLYGON ((13.80961103741604 51.04076975651729, 13.80965521888065 51.04079016168103, 13.80963851766593 51.04080454197601, 13.80959433642561 51.04078412781548, 13.80961103741604 51.04076975651729))',
1: 'POLYGON ((13.80977831740752 51.04313480566009, 13.80987122363639 51.04306085051974, 13.8099989591537 51.04312462457182, 13.80995486494384 51.04315973323087, 13.8099651184249 51.04316486464228, 13.80991634926543 51.04320371166482, 13.80977831740752 51.04313480566009))'}}
gdf1 = gpd.GeoDataFrame(pd.DataFrame(d1), geometry=gpd.GeoSeries.from_wkt(pd.DataFrame(d1)['geometry']), crs="EPSG:4326")
d2 = {'geometry': {1: 'POLYGON ((13.80894179055831 51.04544128170094, 13.80952887156242 51.0450399782091, 13.80954152432486 51.04504668985658, 13.80896834397535 51.04545611172818, 13.80894179055831 51.04544128170094))'}}
gdf2 = gpd.GeoDataFrame(pd.DataFrame(d2), geometry=gpd.GeoSeries.from_wkt(pd.DataFrame(d2)['geometry']), crs="EPSG:4326")
layout = gv.Polygons(gdf1, group="group1") * gv.Polygons(gdf2, group="group2")
layout.opts(
opts.Polygons('group1', cmap=['red'], edgecolor='black', linewidth=0.5, xaxis=None, yaxis=None, backend="matplotlib"),
opts.Polygons('group2', cmap=['lightblue'], edgecolor='blue', linewidth=0.5, backend="matplotlib"),
opts.Overlay(fig_size=500, backend='matplotlib')
)
gv.output(layout, backend='matplotlib')
gv.save(layout, "test.svg", dpi=600, backend='matplotlib')
Screenshot of the observed behaviour
This is a screen from the full dataset.
Expected behaviour
The red fill polygons belong to gdf1 and should have a black edgecolor but it's light blue instead. The blue fill polygon belongs to gdf2 and should have a lightblue fill and blue edgecolor, though the same color seems to be applied to both fill and edge.
What I've tried
Instead of using the group= parameter to specify styling for each of the Polygon elements (which I accidentally stumbled upon through the datashader documentation), I tried making multiple opts calls 'in-line' as suggested in the documentation for HoloViews here. This also has no effect.
Also, cmap=['color'] is the only method I've found to work to have GeoViews not use the automatically detected 'use' column in gdf1 as a vdim for color mapping. Is this the canonical approach and/or expected behaviour? color= or facecolor= seems to have no effect even though they are listed when calling gv.help(gv.opts.Polygons).
In short, I don't understand how to apply these particular styling parameters for the matplotlib backend and would very much appreciate any pointers.
2-Aug-21 Edit
Another strange behaviour seems to be that the figure in the, in my case VSCode-Python, interpreter, where the symbology seems to be faithfully represented, looks different from the .svg output generated by gv.save(layout, "test.svg", dpi=600, backend='matlplotlib'). The below images are outputs from the same run of the script.
Interpreter output:
gv.save() output:
