BUG: colorbar did not match normalised colors

[martinfleis]

In current version, if you use normalisation, colorbar does not represent true color scheme as it is always normalized linear between min and max. This PR fixes the behaviour and normalises colorbar using the same scheme, so the results should match.

It should resolve issue like #697 (comment) .

gdf = gpd.read_file(gpd.datasets.get_path('naturalearth_lowres'))
gdf['random'] = np.random.gamma(2, 2, len(gdf)) - 2

vmin, vmax, vcenter = gdf.random.min(), gdf.random.max(), 0
divnorm = colors.DivergingNorm(vmin=vmin, vcenter=vcenter, vmax=vmax)

gdf.plot(column='random', cmap='RdBu', legend=True, norm=divnorm)

Before:

After:

Closes #697

[codecov]

Codecov Report

Merging #1089 into master will decrease coverage by 1.94%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1089      +/-   ##
==========================================
- Coverage    90.2%   88.25%   -1.95%     
==========================================
  Files          19       19              
  Lines        1837     1839       +2     
==========================================
- Hits         1657     1623      -34     
- Misses        180      216      +36

Impacted Files	Coverage Δ
geopandas/plotting.py	92.5% <100%> (-0.78%)	⬇️
geopandas/tools/crs.py	48.14% <0%> (-37.04%)	⬇️
geopandas/io/file.py	80% <0%> (-14.74%)	⬇️
geopandas/io/sql.py	82.14% <0%> (-14.29%)	⬇️
geopandas/_compat.py	85.71% <0%> (-14.29%)	⬇️
geopandas/geodataframe.py	97.11% <0%> (-0.83%)	⬇️
geopandas/geoseries.py	96.91% <0%> (-0.62%)	⬇️
geopandas/array.py	94.07% <0%> (-0.52%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 8c42164...24b08a0. Read the comment docs.

[codecov]

Codecov Report

Merging #1089 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1089      +/-   ##
==========================================
+ Coverage   89.67%   89.71%   +0.03%     
==========================================
  Files          20       20              
  Lines        1967     1973       +6     
==========================================
+ Hits         1764     1770       +6     
  Misses        203      203

Impacted Files	Coverage Δ
geopandas/plotting.py	92.15% <100%> (+0.06%)	⬆️
geopandas/array.py	93.55% <0%> (+0.06%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f6b835c...a270293. Read the comment docs.

[martinfleis]

Probably resolves #393, but that issue is super unclear.

[jorisvandenbossche]

Fixed the conflict after merging the other PR

[jorisvandenbossche]

This is giving some errors. It might be that the test needs to be updated now the other PR is merged.

[martinfleis]

Tests should be fixed now. I'll wait for CI and merge.