choropleth_example.py

# -*- coding: utf-8 -*-

"""
Choropleth example with Dash

Example using data on Limited English Proficiency in Portland.
Shapefile taken from:

https://gis-pdx.opendata.arcgis.com/datasets/a0e5ed95749d4181abfb2a7a2c98d7ef_121
"""

import json

import dash
import dash_core_components as dcc
import dash_html_components as html
import geopandas as gpd

import matplotlib
import matplotlib.cm as cm

mapbox_key = None
if not mapbox_key:
    raise RuntimeError("Mapbox key not specified! Edit this file and add it.")

# Example shapefile from:
# https://gis-pdx.opendata.arcgis.com/datasets/a0e5ed95749d4181abfb2a7a2c98d7ef_121
# Portland Limited English Proficiency
lep_shp = 'data/lep/Limited_English_Proficiency.shp'
lep_df = gpd.read_file(lep_shp)

# Generate centroids for each polygon to use as marker locations
lep_df['lon_lat'] = lep_df['geometry'].apply(lambda row: row.centroid)
lep_df['LON'] = lep_df['lon_lat'].apply(lambda row: row.x)
lep_df['LAT'] = lep_df['lon_lat'].apply(lambda row: row.y)
lep_df = lep_df.drop('lon_lat', axis=1)

lon = lep_df['LON'][0]
lat = lep_df['LAT'][0]

# Get list of languages given in the shapefile
langs = [lng for lng in lep_df.columns
         if lng.istitle() and
         lng not in ['Id', 'Id2', 'Total_Pop_', 'Geography'] and
         'Shape' not in lng]

# Generate stats for example
lep_df['NUM_LEP'] = lep_df[langs].sum(axis=1)

# Create hover info text
lep_df['HOVER'] = 'Geography: ' + lep_df.Geography + \
    '<br /> Num. LEP:' + lep_df.NUM_LEP.astype(str)

mcolors = matplotlib.colors


def set_overlay_colors(dataset):
    """Create overlay colors based on values

    :param dataset: gpd.Series, array of values to map colors to

    :returns: dict, hex color value for each language or index value
    """
    minima = dataset.min()
    maxima = dataset.max()
    norm = mcolors.Normalize(vmin=minima, vmax=maxima, clip=True)
    mapper = cm.ScalarMappable(norm=norm, cmap=cm.inferno)
    colors = [mcolors.to_hex(mapper.to_rgba(v)) for v in dataset]

    overlay_color = {
        idx: shade
        for idx, shade in zip(dataset.index, colors)
    }

    return overlay_color
# End set_overlay_colors()


# Create layer options that get displayed to the user in the dropdown
all_opt = {'label': 'All', 'value': 'All'}
opts = [{'label': lng.title(), 'value': lng} for lng in langs]
opts.append(all_opt)

# template for map
map_layout = {
    'title': 'Portland LEP',
    'data': [{
        'lon': lep_df['LON'],
        'lat': lep_df['LAT'],
        'mode': 'markers',
        'marker': {
            'opacity': 0.0,
        },
        'type': 'scattermapbox',
        'name': 'Portland LEP',
        'text': lep_df['HOVER'],
        'hoverinfo': 'text',
        'showlegend': True,
    }],
    'layout': {
        'autosize': True,
        'hovermode': 'closest',
        'margin': {'l': 0, 'r': 0, 'b': 0, 't': 0},
        'mapbox': {
            'accesstoken': mapbox_key,
            'center': {
                'lat': lat,
                'lon': lon
            },
            'zoom': 8.0,
            'bearing': 0.0,
            'pitch': 0.0,
        },
    }
}

app = dash.Dash()

app.layout = html.Div([
    html.H1(children='Portland - Limited English Proficiency (Choropleth Example)'),
    dcc.Dropdown(
        id='overlay-choice',
        options=opts,
        value='All'
    ),
    html.Div([
        dcc.Graph(id='map-display'),
    ])
])


@app.callback(
    dash.dependencies.Output('map-display', 'figure'),
    [dash.dependencies.Input('overlay-choice', 'value')])
def update_map(overlay_choice):

    tmp = map_layout.copy()
    if overlay_choice == 'All':
        dataset = lep_df
        colors = set_overlay_colors(lep_df.NUM_LEP)
        tmp['data'][0]['text'] = lep_df['HOVER']
    else:
        dataset = lep_df.loc[lep_df[overlay_choice] > 0, :]

        colors = set_overlay_colors(dataset[overlay_choice])

        # Update hovertext display
        hovertext = lep_df['Geography'].str.cat(
                        lep_df[overlay_choice].astype(str), sep=': ')
        tmp['data'][0]['text'] = hovertext
    # End if

    # Create a layer for each region colored by LEP value
    layers = [{
        'name': overlay_choice,
        'source': json.loads(dataset.loc[dataset.index == i, :].to_json()),
        'sourcetype': 'geojson',
        'type': 'fill',
        'opacity': 1.0,
        'color': colors[i]
    } for i in dataset.index]

    tmp['layout']['mapbox']['layers'] = layers

    return tmp
# End update_map()


if __name__ == '__main__':
    app.run_server(debug=True, port=8051)