Add support for legend_field with geo data

ALL software version info (bokeh, python, notebook, OS, browser, any other relevant packages)

• bokeh version 1.4.0
• python 3.7
• Windows 10

Description of expected behavior and the observed behavior

I want to add a legend to my plot of Geodata. In particular, I plot point data with different coloring according to a categorical variable in my data set. I transform my geopandas to to a GeoJsonDataSource accordingly. Everything works well, except creating the legend.

When I follow the following example: https://docs.bokeh.org/en/latest/docs/user_guide/annotations.html#legends I get the following error:

Column to be grouped does not exist in glyph data source.

Even though I include the source in the glyph method, i.e.

p1.circle(
    "x",
    "y",
    source=geosource,
    fill_color={"field": "share_prot", "transform": color_mapper},
    line_color="black",
    line_alpha=0.5,
    line_width=0.3,
    alpha=0.6,
    #size=2,
    legend_group="share_prot"
)

Complete, minimal, self-contained example code that reproduces the issue

from bokeh.io import output_file, show
from bokeh.models import GeoJSONDataSource
from bokeh.plotting import figure
from bokeh.sampledata.sample_geojson import geojson
import json

data = json.loads(geojson)
for i in range(len(data['features'])):
    data['features'][i]['properties']['Color'] = ['blue', 'red'][i%2]

geo_source = GeoJSONDataSource(geojson=json.dumps(data))
p = figure(background_fill_color="lightgrey")
p.circle(x='x', y='y', size=15, color='Color', alpha=0.7, source=geo_source, legend_group='Color')

show(p)

Stack traceback and/or browser JavaScript console output

<ipython-input-133-afa857e8c002> in <module>
     12 color_mapper = CategoricalColorMapper(factors=share_prot.unique(), palette=palette)
     13 p = figure(background_fill_color="lightgrey")
---> 14 p.circle(x='x', y='y', size=15, color='Color', alpha=0.7, source=geo_source, legend_group='Color')
     15 
     16 show(p)

fakesource in circle(self, x, y, **kwargs)

~\Anaconda3\envs\adv\lib\site-packages\bokeh\plotting\helpers.py in func(self, **kwargs)
    930 
    931         if legend_kwarg:
--> 932             _update_legend(self, legend_kwarg, glyph_renderer)
    933 
    934         self.renderers.append(glyph_renderer)

~\Anaconda3\envs\adv\lib\site-packages\bokeh\plotting\helpers.py in _update_legend(plot, legend_kwarg, glyph_renderer)
    487     kwarg, value = list(legend_kwarg.items())[0]
    488 
--> 489     _LEGEND_KWARG_HANDLERS[kwarg](value, legend, glyph_renderer)
    490 
    491 

~\Anaconda3\envs\adv\lib\site-packages\bokeh\plotting\helpers.py in _handle_legend_group(label, legend, glyph_renderer)
    454         raise ValueError("Cannot use 'legend_group' on a glyph without a data source already configured")
    455     if not (hasattr(source, 'column_names') and label in source.column_names):
--> 456         raise ValueError("Column to be grouped does not exist in glyph data source")
    457 
    458     column = source.data[label]

ValueError: Column to be grouped does not exist in glyph data source

[hmanuel1]

I ran into the same issue with the custom legend for geopandas. This is working somewhat for me. It will work if you don’t expect x_range or y_range to change. Trying to figure out how to prevent the “fake quads” from rendering, so it will not affect x_range or y_range when replacing the content of a figure. It will be nice that manual legends can be implemented without having to specify an actual coordinate pair in the plot.

from bokeh.io import show
from bokeh.models import LogColorMapper, Legend
from bokeh.palettes import Viridis6 as palette
from bokeh.plotting import figure
from bokeh.sampledata.unemployment import data as unemployment
from bokeh.sampledata.us_counties import data as counties

palette = tuple(reversed(palette))

counties = {
    code: county for code, county in counties.items() if county["state"] == "tx"
}

county_xs = [county["lons"] for county in counties.values()]
county_ys = [county["lats"] for county in counties.values()]

county_names = [county['name'] for county in counties.values()]
county_rates = [unemployment[county_id] for county_id in counties]
color_mapper = LogColorMapper(palette=palette)

data=dict(
    x=county_xs,
    y=county_ys,
    name=county_names,
    rate=county_rates,
)

TOOLS = "pan,wheel_zoom,reset,hover,save"

p = figure(
    title="Texas Unemployment, 2009", tools=TOOLS,
    x_axis_location=None, y_axis_location=None,
    tooltips=[
        ("Name", "@name"), ("Unemployment rate", "@rate%"), ("(Long, Lat)", "($x, $y)")
    ])
p.grid.grid_line_color = None
p.hover.point_policy = "follow_mouse"

p.patches('x', 'y', source=data,
          fill_color={'field': 'rate', 'transform': color_mapper},
          fill_alpha=0.7, line_color="white", line_width=0.5)

"""
 custom geo legend that works with this example
 with geopandas dataframe see the next commented block
"""
xq, yq = data['x'][0][0], data['y'][0][0]

"""
 for geopandas dataframe you can do the same by selecting a coord of a valid polygon
 the following line will take the coordinate pair xq and yq from a
 geopandas dataframe (gdf) polygon...
(xq, yq) = list(gdf['geometry'].values[0].envelope.centroid.coords)[0]
"""

legend_names = []
for i in range(len(palette)):
    legend_names.append(f"Legend Item {i}")

items = []
for i in reversed(range(len(palette))):
    items += [(legend_names[i], [p.quad(top=yq, bottom=yq, left=xq,
              right=xq, fill_color=palette[i])])]

p.add_layout(Legend(items=items, location='bottom_left',
             title="Unemployment Rate:"))

show(p)

[meenurajapandian]

I came across this while looking for a way to add a legend to a heatmap with a linear colormapper that uses a GeoJSONDataSource. But the legend_field does not work for me either.

The figure is basically this: p.patches('xs', 'ys', fill_color={'field': 'some_field', 'transform': mapper}, source=geo_src, legend_field='some_field')

some_field is a feature of each patch and geo_src is a GeoJSONDataSource. Color is mapped as required but not able to add legend. Is there a work around to get the legend?